I had this issue with my R32. The mirror dipping is active but you have not set it yet. Here is how to do it.
1 - Start car and put her in neutral (easy that one)
2 - On your mirror control set the knob to L for control of the passenger door mirror
3 - Put the clutch in and put the car into reverse. Keep the clutch in and keep in reverse.
4 - Use the mirror knob control to adjust the level of dip you want for when the car is in reverse
5 - When done select 1st, drive off or whatever you want to do and the mirror will rise back up to the normal non reverse position
6 - Now in my R32 the mirror would then only auto-dip in reverse when the mirror control is left sitting on the 'L' position. That is, for example, if I had the mirror control set to R, Heaters or 0 and put the car in reverse the mirror will not dip. Flick it onto L however and it will dip as it is supposed to

Hope this helps.