Reset service light indicator, engine oil life Audi A4, year: 2001-2007, oil reset instructions:

For Fixed Interval servicing, you can use the following procedure:

Below and to the right of the speedometer are three buttons – the right-hand button of these three is usually labelled “0,0”, and the centre button labelled with a spanner/wrench symbol.
Start with the key in, but the ignition turned OFF
Press and hold the Spanner button, while turning the ignition on (position 2)
Release the Spanner button
“SERVICE” should now appear on the display
Press and hold the 0,0 button until the display shows “SERVICE IN xxxx Miles / Kilometres”
Release the 0,0 button, then turn off the ignition