Reset service light indicator, engine oil life Mercedes Benz Vito, year: 2002, oil reset instructions:

Turn the key to position 2in the steering lock and immediately press the KM button twice briefly.
Within 10 seconds, turn the key back to position 0 in the steering lock.

Press and hold down the KM button. Turn the key to position 2 in the steering lock. Hold the KM button down for a further 10 seconds.

The service indicator with current remaining distance/remaining time appears.

After about 10 seconds, an acoustic signal will sound and the service displaywith the new remaining distance/remaining time will appear for about 10 seconds.

Relaese the KM button.

All quoted direct from the handbook! It took me a couple of goes to get it to reset (lack of counting ability maybe!) but I got it reset in the end.