There is a snall hole in the bottom of the mirror housing, this allows you to turn the mirror holder and release or lock the mirror in position. when you look in the hole you will see a small slot( I beleive there are two slots one for the locked postiton and one for the unlocked) and that is where you put the slot of the screwdriver. They do not usually come loose unless they have been knocked about. You should use a small screwdriver to turn the mirror lock, it moves about a quarter of an inch. Take a look at the way it works when the mirror is out first to make sure yoou tunr it the right way and to get a better idea how it works.