Hey Markus,
It is not possible to change the bookings app widgets using code but you can set up what you are looking for without code.
To do this go to your Mobile Editor, select the booking services widget and click settings.
Once you are in the settings go to Layouts and where is says “Show categories as”, select tabs instead of dropdown and it will be the same as the desktop version.
Hope this helps!
Dara | Corvid Team