I think you can only change your Username via the Volkswagen App on your phone or PC.
It's actually my Nickname and not my Username that appears on the Infotainment Screen, when I get into my vehicle. If you wish to change yours try the following:
Log on to your User account within the VW App
>Go to
Profile and Settings >Open
Volkswagen ID >Go to
Edit Data >Change your
"Username" and/or
"Nickname" and then click
"Save".
At least that's how I did it and the next time I jumped into my car, the edited information was on screen. Good luck!
