Hello. Under the Available Tasks, Assign the Disk as a Global Hot Spare. It will automatically rebuild and join the array.
What this is showing is the working 3TB in slot 1 and I have replaced the 3TB in slot 0 with same make from DELL and that drive shows ready but how do I get the rebuild going? This is what the Physical Disk shows and s/n 9XK0K5CL is the new disk that needs to be rebuilt. 
T320 Perc 710 raid 1 disk Replacement