Servicing can be done anywhere, and by anyone (including yourself). That's the same for Mercedes as well as other makes, and for the B service as well as A or C or whatever.
Resetting the service indicator is not difficult, can't tell you how exactly to do it, since you don't mention what model or year your car is (!!), so you'll have to google it yourself.
Having said which...
1) If the car is under warranty, this may become void if you don't have the car serviced by an approved service provider.
2) Having the car serviced by someone who doesn't know what they're doing is a false economy, and probably causes more problems than it's worth. My personal opinion is, if you buy a premium car like Mercedes, you need to get it serviced by Mercedes - otherwise, buy a Kia!
3) In the specific case of Mercedes-Benz, the 'Mobilo Life' road assistance etc. service will be discontinued if the car is not serviced as Mercedes requires.
UPDATE: Actually, ignore my answer, I now realise you're just some idiot troll who's copied & pasted word-for-word this old question from ten years ago:
https://answersrip.com/question/index?qid=20070214125242AATwxii
Get a life, loser!