Now you should see a black material covering the door. This is called a vapor panel and protects the innards of the door form water and moisture. It should peel right off, but don't be afraid to use the screwdriver to gain leverage.
You will find another small connector similar to those found when disconnecting the window control panel. This operates the powered mirror and must be disconnected before the mirror is unscrewed.
Remove the small triangular portion of the vapor plate where the mirror mounts, you should see 3 large holes, inside which are the mounting screws for the mirror.