In the wild, it is in a puppy’s nature to bark, nip and invade other pack members space to play and see where they fit in the pack . When a pup play bites or nips another wolf they will get a mouth full of fur. When a domestic puppy nips a human’s bare flesh with their pin sharp teeth it can hurt. To make it completely clear to your pup that play biting is not a welcome behaviour – you should take them by the collar, each time they nip you, and move them back a couple of meters without looking or speaking to them. If your pup persists on play biting repeat the action but move them back a bit further to make the message clearer, that you do not wish to engage in this game. If your puppy still persists take it a step further by isolating them in another room where they cannot see you. This will give them time for their state to calm and the opportunity to think about the consequence of their actions. When your pup is calm, let them out and go back to what you were doing. If your dog comes over and attempts to carry on with the play biting , repeat the isolation method until your puppy gives up.
As leader you decide when it is time to interact and teach your dog manners in play.
Once the dog is calm and has left you alone, you can teach them a desired response by calling them into your space and show them what is allowed for example cuddling or light playing. If they then again become too excitable and bite, repeat the method until they realise they took it too far.
In this scenario of moving the pup away (and isolating if necessary) each time it nips you, someone has to give up. Do not let it be you. I have had a severe case where I have had to isolate a dog over forty times in one day because they believed they dictated when to interact and had no manners. Eventually the dog got the message. Your reaction should always be calm, convincing and consistent by never giving up. You cannot fail.