You also have to set the mirror to the position you want it to go to when selecting reverse. It sounds like it hasn't actually been setup yet.
Put the dial to L and car in reverse. Adjust the mirror to where you want it to go. That should it be it set.
Put it out of reverse and back in to see if its worked.
I remember reading a post of someone mirror pointing up the way when they put it into reverse. They thought the set up was broke but it was probably just some joker set it to that for a laugh.
Oh and like Snoopy has said, the dial has to be set to the L position for it to work automatically when you put it in reverse.