How do you reset Mercedes c class key?

"Put the key in the ignition push the lock button on your keyfob, pull the key out while holding down the lock button and press the unlock button 5 times. Your key is now reset and ready for use

this also works for the Mercedes E200 keyfob, as tried and tested successfully!

It works on a 98 SLK230. The ignition needs to be turned on and the car started before pressing and holding lock then pressing unlock five times."

Hope that helped a bit, cuz personally I don't own a Mercedes C Class, but I have tried with my Opel Astra few years ago and it worked out pretty well. So give it a try as the other user has described above!

As seen in: How_do_you_reset_a_Mercedes_key_fob