1. Turn the ignition key to position 1 (accessory mode) without starting the engine.
2. Press and hold the "CLR" button on the left side of the instrument cluster until the display reads "Reset."
3. Press and hold the "BC" button on the left side of the instrument cluster until the display reads "Service Reset."
4. Turn the ignition key to position 0 (off) and then back to position 1 (accessory mode).
5. The service light should now be reset.
If the service light does not reset, you may need to take your vehicle to a Mercedes-Benz dealership or qualified repair shop to have it reset.