How to Rethread a Roller Blind Cord
It's easy to replace the chain or cord on roller blinds that have become loose or so worn that they need to be replaced. To rethread a roller blind rope cord, start by removing the blinds from the wall and popping out the clutch, which is the case with the cord in it. Next, pull the cord out of the clutch the rest of the way. Then, make a 1-inch loop with the cord, hold the clutch with the base facing down, and slide the loop under the guard until it comes out on top of the pulley teeth. Take the cord by the loop and pull it out far enough so you can slip it down over the barrel. You can then push the cord into the pulley teeth. Rotate the pulley teeth clockwise as you gently tug down on any cord that bunches up between the guard and barrel. Finally, insert the clutch back into the blinds and hang them back up.
Remove the blinds from the wall and pop out the clutch. Most roller blinds will have a little pin on the side opposite the cord. You can push this pin in with a flat-head screwdriver. This will release the blinds, allowing you to pull them off of the mount. Once you have the blinds off, pop the clutch (the part with the chain) off. Use a flat-head screwdriver to pop the clutch off, if needed. This method is meant for blinds that have ball-and-chain style cords; they look similar to the chains found on key chains and dog tag necklaces. Pull the chain out. Search the chain for the connector first. Depending on the style, you may be able to pop one of the ends out of the connector. Sometimes, however, you will have to pop open the connector, then pull the chains out. Put the connector into a safe place so that you don't lose it. Thread one end of the chain up through the guard. Hold the clutch with the barrel facing upwards and the base facing down. Slide the tip of the chain through the left side of the guard. Press the chain into the pulley teeth. Hold about an inch (2.54 centimeters) of so of the chain against the pulley teeth. Press down on it with your thumb until they pop into place. Rotate the pulley teeth and pop the chain into place. Keep rotating the pulley and popping the chain in bit-by-bit until the tip of the chain reaches the left side of the guard. Pull the chain through the clutch. Rotate the pulley teeth until the chain comes out of the right side of the guard. Grip the chain with your fingers or a pair of pliers, then pull down on it. The chain should now be fed through the clutch, with both ends dangling out of the clutch. Reassemble the blinds and hang them back up. Pop the clutch back into the blinds first, then hang the blinds back up on the wall. Reassemble the chain. Feed the chain through the bottom roller, then bring both ends together. If this is a new chain, you may need to trim it down first. Fit the connector over both ends, then snap it shut. If this is a new cord, you may need to trim it down first. Remove the blinds and the clutch. Most roller blinds will have a pin that you push in with a flat-head screwdriver. This will release the blinds, allowing you to pull them out. Once you have the blinds off, use a flat-head screwdriver to pop off the clutch (the case with the cord in it). The release pin is typically on the side without the cord. Pull the cord out of the clutch the rest of the way. Save the cord, or get a new one intended for the type of roller blind you got. If the cord is already pulled out of the clutch, then you and skip this step. Push a loop of cord up through the guard. Make a 1-inch (2.54-centimeter) loop with the cord. Hold the clutch with the base facing down and the barrel facing up. Slide the loop under the guard so that it comes out on top of the pulley teeth. Pull the loop over the barrel. Take the cord by the loop and pull it out far enough so that it can fit over the barrel. Slip the cord down over the barrel. Push the cord into the pulley teeth with your thumb. As you push the cord down, it may start to bunch up at the right side. Gently tug the cord downward to smooth as it as you push it into the teeth. Rotate the pulley teeth clockwise. The easiest way to do this would be with a pencil eraser, but you can do it with your pinky finger too. Hold a pencil, eraser-side-down, against the pulley teeth. Use the pencil to rotate the pulley teeth clockwise. Gently tug down on any cord that bunches up between the guard and the barrel. Insert the clutch back into the blinds. Hang the blinds back up, then test the cord out. If the cord is not connected, you will need to adjust the length, trim off the excess, then attach the connector. Remove the blinds from the wall and pull the clutch off. Unlike other types of clutches, this one appears to be solid. You cannot see the pulley teeth because they are inside the clutch. To remove the blinds and the clutch, do the following: Use a flat-head screw driver to push the release pin. You can typically find it on the side without the cord/chain. Life the blinds off of the wall mount. Pop the clutch off; use a flat-head screwdriver if necessary. Pinch the pins together at the top of the clutch. Hold your hand against the bottom of the clutch while you do this. Pinching the pins will release the base of the clutch, and cause it to slide out. Slide the base of the clutch out. Depending on the brand, the base may slide out all the way, or it may slide out partway. If you have the first type, only slide the base out far enough so that you can see the pulley teeth and the chain. Pull the chain out. If you are going to thread a new chain, take this time to get it out. Do not cut down the new chain down just yet, however. Loop the chain around the roller teeth. Make a loop with the chain big enough to fit over the base. Drape the chain around the base. Make sure that the ends of the chain come out of the notched part on the clutch. Slide the clutch shut. Some clutches snap shut on their own. Others have a pin at the bottom that you need to push in to lock the two pieces together. Reassemble the blinds. Pop the clutch back into the blinds, then hang the blinds back up. Loop the chain around the bottom roller, and adjust the length, if needed. You can adjust the length by opening the connector on the chain, trimming the chain down, then snapping the connector back shut. 
Remove the blinds from the wall and pop out the clutch. Pull the chain out. Thread one end of the chain up through the guard. Press the chain into the pulley teeth. Rotate the pulley teeth and pop the chain into place. Pull the chain through the clutch. Reassemble the blinds and hang them back up. Reassemble the chain. Remove the blinds and the clutch. Pull the cord out of the clutch the rest of the way. Push a loop of cord up through the guard. Pull the loop over the barrel. Push the cord into the pulley teeth with your thumb. Rotate the pulley teeth clockwise. Insert the clutch back into the blinds. Remove the blinds from the wall and pull the clutch off. Pinch the pins together at the top of the clutch. Slide the base of the clutch out. Pull the chain out. Loop the chain around the roller teeth. Slide the clutch shut. Reassemble the blinds. 