There are 114 of these mirrors in the game. *Do not use either of the other two (see Known Issues). A box will pop up and the middle option is the one to choose. Simply activate it to revise your character. In the image gallery you'll see which one I've used, the more intact one.
There are three types of mirrors in the game. Revise your character no matter what level you are, without resetting your stats, skills, traits and perks simply by activating a mirror.