I assume you have the very pretty Intelligent Lighting Systems.
If it one of the very white thin lights then it is a LED, and is not replaceable. But it may not be that that has failed, there is a LED driver (on the bottom of the headlight, so its a headlight out job, i.e bumper off) that can fail too.
Are you out of the 3 year warranty? Even if you are, this may be worth asking Mercedes for goodwill replacement as you can't be far out of the 3 year warranty
Richard