I just got a puppy and his area where his umbilical cord was is like inflated with air, will that go down?

i don't know exactly if it air or a liquid...the puppy is 6 weeks from what the breeder told me...and the puppy is a pit bull/bull mastiff mix(supposedly if it isn't bull mastiff it is some kind of mastiff, because the father is supposed to be pit bull/bull mastiff and the mother is pit bull)