What can i do if my puppy wont eat?

So I just got a 6week puppy! He drinks formula milk. But he won't eat dry soild food that is for puppy. He would eat canned food but have him diarreahia so I stoped! Today I bought him kibble n bits Mini he won't eat it either. A person told me to mix kibbles with his milk? How do I get him 2 eat?