Leave him/her but keep an eye out. Then if after a few hours its still not breathing properly I would ring the vets just to ask a few questions and then if the vet can not go on the phone you should just go there, it would not harm the puppy it could be its first check up which is good.
Clean out the nose and mouth with a thingie that you would clean out a baby's nose or mouth out with.
Then, if that doesn't work..
VET VET VET VET VET VET VET!
VET...VET...VET! It may be a birth defect, but it could also have aspirated birth fluid...VET!!
phrannie10 week old puppy is having trouble breathing
Take it to the vet immediately.Why does my dog keep bringing me her newborn puppies?
take them to the vet asap if not and you wait your pup may die this could be very serious I know from experience so please get to a vet right now!!!How long does it take for a dog to have puppies?