...to make it tilt down a bit when reversing in order to get a better view of the curb when parallel parking? It's not in the COMAND Vehicle settings that I can see (2018 C300 4Matic sports sedan).
As far i can remember you can adjust it something like this.
Try to push the passenger side mirror know so it lights up red
Put your car in reverse
Adjust the mirror
set car in Park.
Try to set car in reverse again,, see if it works now.
Next time you sit in the vehicle, put it in Reverse with your foot on the brake.
Now while still braked, press the left or right side mirror button
Then adjust the mirror as you want it when having to reverse every time.
Once complete, put the car into drive with brake pedal still pressed.
Then adjust that same mirror back to normal viewing as when you need it to drive.
Turn off the vehicle.
Then restart, put in Reverse and see if that works.