rice and chicken or fish for a day or two until tum starts to settle down - you can buy pet mince for 90p or so at pets at home, frozen in a block - should last two days as main meal with rice, but stick to white meat (turkey doesnt agree with my pup).
If puppy is still squitty after a day or two, take to vet please as they can get very dehydrated. Also may have a bug or paracite causing tummy upset
How old is pup? I think many breeders send them off too early, before they are fully weaned. poor little things.
We have always given puppy own food for first week, then gradually introduce new food over the next two weeks, in ever increasing proportions (90:10 old to new > 80:20 etc).