You do nothing because you can’t do anything.

Only the passenger side mirror tilts when the button on the switch is in the
correct position and you put the
gear shift lever in reverse. If I’m incorrect, then the description of the driver’s mirror tilt feature will be listed in your owners manual.…but again, I’ve never seen the driver’s side mirror tilt when in reverse unless the driver manually manipulates the mirror themselves.
Also see the last sentence in the
“principle of operation“ info in post #22 above where it only mentions the passenger side mirror tilting when reverse is selected and the switch is set to the driver’s side.
This is a feature that has been on BMWs for multiple decades (like the 1970s & 80s). The driver’s side mirrror has never tilted when reverse is selected. It has always only been the passenger mirror that tilts…to help the driver know where the curb is located on the passenger side.
Info from my 1985 e30, 1991 e32, & 1995 e34 owners manual:
Info from my 1997 e38 & 1999 e39:
Info from my 2006 e53 X5:
Info from my 2013 f06 & 2014 f15 X5: