I have a 3 1/2 month old mini dachshund. I have had him for 5 days now and hes not eating very good.?

where we got him she fed him purina alpo adult hard food, i didnt think that was good so i got a bag of pedigree small dogs and he wont eat that. so we used to alpo with some hot water and scrambled some egg and he only eats a tiny bit. what food do you think he should be on obviously puppy so he gets the nutrients he needs. i have a petsmart and petco where i live any thoughts? thank you