I would not take him out to a groomer until he's finished his full vaccines. 7 weeks is soooooooo young. I don't even start the first vaccines until they are 9 weeks.
I'd just wipe him off if needed and wait a couple weeks. but if he absolutley needs one make sure to do it in a warm room and keep him warm after and carefully dry him.
Is he your first puppy? How's he eating for you at 7 weeks? Lots of info here on YT. Lots
At 7 weeks mine are still nursing and eating on their own so make sure he's eating real well
