To reset the 1998 Audi A6 service inspection light after a oil change, please follow these instructions:

Manual Reset using Odometer and Reset Knobs:
1. Turn off the ignition.
2. Locate the Service Interval Display, which is below the odometer.
3. Do the following to display the service OIL message in the Service interval display:
i) Press and hold the TRIP ODOMETER RESET knob.
ii) Turn on the ignition – do not start the engine.
iii) Release the TRIP ODOMETER RESET knob.
4. Pull out the CLOCK ADJUSTMENT knob.
5. Press and hold the TRIP ODOMETER RESET knob until the message changes to service INSP, then release the knob.
6. Pull out the CLOCK ADJUSTMENT knob, hold for 2 seconds and release.
7. Turn off the ignition.
8. Start the engine and verify indicator has been reset.