Go to RAID Properties>Manage Array>Manage Hot Spares. You should see a list of all of the drives the controller detects. The drives in your RAID 1 will be listed as Primary and Secondary. The new drive should not have anything in the "Drive Status" field. Use the arrow keys to highlight the new drive and the +/- keys to assign it as a hot spare. After you assign it as a hot spare it should start rebuilding.
If you do not see the drive in that list then check the SAS Topology screen. If you see it in SAS Topology then use CTL D to pull up additional options. Let me know if it will allow you to do anything to the drive in that screen. If you don't see it in SAS Topology then it does not appear the controller is able to properly communicate with this drive.
Dell EMC, Enterprise Engineer