cant get e chrome off my old mirror assm.. yes the 4 screws are out, and, ive done it b4!!

I don't remember how to remove the mirror to get the cover off!! and I tried for an hour.
I got a black one with my new door. finally got the door finished. id love black but don't have 2.

 

I remember reading about this b4 and now after an hr searching cant find anything.
no help from the forum?
is it dying?