Hi
If you are talking about the top left as you look from underneath, then you will see that there is a blanking plate to the rear which you remove to fit an expansion port like the SCSIKit for the Blizzard Turbo and the plate is screwed into position through that hole.
http://www.commodore-amiga-retro.com/amiga/a_scuzz_nov02/a_scuzz_nov02_221.jpgThe other is located directly below the screw to the motherboard.
