1. Turn on the ignition, but do not start the engine.
2. Press and hold the "0.0/SET" button on the instrument cluster until the service indicator appears.
3. Turn the ignition off.
4. Press the instrument cluster button again.
5. Push reset for more than 2 seconds.
6. Turn the ignition back on.
7. The service indicator should now be reset.
This procedure may vary slightly depending on your specific Audi A3 model. If you are unsure how to reset the service light, you can always consult your vehicle's owner's manual or take it to an authorized Audi dealership for service.