just make sure you do not take it home early because fully weaned. The time it has now playing with the other puppies is important

>My question is what to do?

A pup I bought had to be weaned early and the litter separated from the mum after she disappeared after a pheasant during exercise when the litter was 3 weeks old, and wasn't found (injured on the central reservation of the motorway) till a couple of days later. Obviously there was no way the mum could look after them, but the breeder was excellent and the pups thrived and had every care. Obviously not ideal but it needn't be a problem.

Catswoody:
Infected teats are not uncommon with nursing mothers. Your Breeder recognised the problem and sought advice & medication was administered. Perhaps separating you assigned puppy was precautionary and the fact the breeder advised of the situation can only be seen as a positive thing.  As Alexandra74 said, any Puppy collected should be checked by your own Vet within
a few days and a reputable breeder will advise this within their Puppy Contract.  Re weaning & worries re socialisation/litter manners - that will still be introduced when your puppy rejoins his/her siblings. Hey this is a happy time - enjoy the build up to your new addition