Here is a cut-and-paste curtosey of one of E-Klasse's earlier posts!
To Start, remove key, close the door, let the dome light go out and the instrument cluster shut down & then start the process.
Key on (position 2, all lights come on, engine NOT running)
PUSH the trip odometer reset button twice RAPIDLY, the time/distance remaining for FSS is shown.
PUSH button in and HOLD it in.
Turn key OFF (DON"T release the button!)
Turn key back to position 2....KEEP holding the button down!
You'll need to hold it down over 10 seconds, you'll hear the beep and 10000 will be the new display. DON'T release the button until you hear the beep, wait at least 15 seconds before deciding on giving up.
The sequence was exactly as described in the owners manual (Make sure you have the doors closed). The trip odometer button needs to be rapidly depress twice at the beginning of the procedure, rather than two deliberate but slower pushes.