I did this today on mine after changing all the fluids and filters. It tells you in the owners manual (which by the way you can buy pdf version online for $9).
Here is your answer.
Following a completed A or B service the
Mercedes-Benz Center sets the counter mileage to
10 000 miles (Canada: 15 000 km).
The counter can also be set by any individual. To do so:
Turn the electronic key in steering lock to position 2.
To call up the trip odometer and main odometer, press
button è or ÿ on the multifunction steering
wheel until the display appears. See page 92.
Press button j or k until the FSS indicator
appears.
Press button J on the instrument cluster for
approximately 4 seconds.
The multifunction display will show the question:
“DO YOU WANT TO RESET SERVICE INTERVAL? –
CONFIRM BY PRESSING R”
Press button J on the instrument cluster again for
approximately 4 seconds, and hold until a signal
sounds. The message “SERVICE INTERVAL HAS BEEN
RESET” appears in the multifunction display.
The new service indicator is displayed with the reset
distance of 10 000 miles (Canada 15 000 km).
If the FSS counter was inadvertently reset, have a
Mercedes-Benz Center correct it.
However you choose to set your reference numbers, the
scheduled services as posted in the Service Booklet
must be followed to properly care for your vehicle.