Phillips or cross head screw driver. And i think there's someone on ebay selling the mirror glass part only.... I needed one - but ended up getting yellow ones!
Ha, ha. I've done that but being able to see through a 3.5mm hole into a black mirror is not a skill I possess.
I did tweak it with a small, straight bladed screwdriver at the weekend but it's a bit of a hassle to locate. I felt it could have been a pozi that I was just picking up on by chance, thus the question.