Whatever you do, never use a screwdriver. That only causes unnecessary scratch- and dent-risk. Use a nylon tool which is much less likely to cause any damage, and also very useful for taking the inside trim apart. It might be easiest to drive by your dealer and ask for a weatherstrip-tool. The cover is clipped on, see the photo below for the locations of the hooks. Taking the entire mirror of is quite easy to do, but the cover isn't that hard to get off either. Start near the left of the picture and work your way around the bottom to unclip the hooks. Just take your time and you'll be fine.