First of all for your own safety and security please do not post a service tag in the forum. The SD reader was an option and if you have it should not be blocked off. Device Manager would have a reference to the reader if you have one. As an alternative you could use an adapter such as one of these.
I got Inspiron 3891 few months back, with .  I'm trying to use SD card reader for the first time.  The slot seems to be blocked off and I can't pull out dummy panel.  Is that because this machine didn't come with a reader?  Or just it is difficult to pull it out?  I tried pushing it to pop it out and also try to pull out with sharp object.  How can I check the spec to see if it even came with one?  Manual only indicates how to install and remove, I can't find the exact spec. 
Missing SD Card reader on new computer