Looks like an easy fix to me. With the unit unplugged and in the same position it's in now, remove the (8) Allen bolts around the plate perimeter. Then, with your hand supporting the plate, tip it over and let the plate slowly drop out. If it doesn't, it's likely stuck to the gasket and you made need to use a pick tool in one of the Allen bolt holes to gently pry it loose. You can also support the back at the top & bottom on 1" thick paperback books so the plate is facing down on your table. In a little while gravity will pull it free. My guess is the small screw(s) that hold the XLR socket inside the shell loosened up and dropped out. Find them, reinstall, and put the plate back in. There is little that can go wrong if you take your time. However if you discover the XLR shell/socket are plastic and broken, the socket will need replacement and that may require soldering & fabrication if an exact XLR cannot be located.