Hello and welcome to just answer
The only way to reset the Airbag light is to use plug in diagnostic equipment to clear the fault memory. Even if the fault has been repaired the control unit will not clear the fault by itself.
You do not have to use an Audi dealer to do this for you as most garages will now have diagnostic equipment which will allow them to clear the memory for you as long as the fault has been repaired.
I hope this helps and if I can help further please feel free to ask