Programming a garage door remote to the mirror Homelink buttons is not described in the VW manual. I read the manual twice and could not find it. There are no references in the index or the table of contents, so i resorted to the instructions that came with the garage door system, which is a Genie for me. Those instructions did not work.
I searched the online manual for "HomeLink" without any success:
Once you know the function is available, download the HomeLink Connect app to your phone:
Once installed, you need to connect the phone app to the mirror via Bluetooth. When it is connected, you will have options to program the button(s) of your choosing to the opener remote. If your opener is a newer model with roving codes, then an additional step is required to click program or learn button on the opener (not the remote).
The app has a walk through of the steps.
Hint: since my opener has a roving code, I did not sit on the driver's seat to turn on the ignition. Rather, while still outside with the door opened, I hit the start/stop button on the steering wheel column to turn on the car. If you sit in the seat and press the brake to start the car, when you get out to hit program/learn on the opener the entire setup is lost and you must start over.