Chow Chow Allergic Reaction?

[nlf1017]

Hi! I’m about to adopt a chow chow puppy I found online and will be driving 3 hours away to see/pick him up. I was told he had an allergic reaction to Bone Healthy food they were feeding him (“rubbing against his nose while eating”). Anyone know the best way to get him back to healthy? They told me they were healing him but I want to ensure I do the proper things to get him better (obviously will be providing better food than they fed him).
Thanks in advance