I am trying to help my dad out. His roommate has a dog that won't eat dry food how can we work on this?

Because the dog knows it's total crap. No, i'm joking. Dogs are smart, and if they refuse what they're given some owners worry and will give them something tastier. The dogs got you well trained ;) Don't give inand take the food away after 15 minutes if it is untouched. Put it down again at the next meal time.