How do you reset the settings to zero you just changed your oil but you want to reset the milage to service on 2001 Mercedes Benz c240?

See your manual for the Flexible Service Schedule rest. It changes in some vehicles but it's something like:
Doors closed.
Turn the key to position 2.
Press the O (mileage reset) button twice.
Turn key to off.
Press and hold the O button while turning the key to position 2.
After about 10 seconds it resets.