I'm trying to tighten a toilet seat in my house which has become loose, the underside is not accessible but the top side has a metal plate that covers a screw which I believe I can tighten, however the metal covering plate is on so tightly that I cannot get it off to access the screw. I've tried working around the edge with a flat-head screwdriver but have had no success. Anybody else have experience with these and have any tips on how I could get them off?