my five months old puppy ate 2qts of food

Question
Wht can we do he has  throw up once

Answer
What kind of a dog is this? If it's a small dog then you should probably induce vomiting with some peroxide. If it's a large dog then you need to watch him for his stomach bloating.

How long ago did he eat it and what kind of food was it? Dog food, people food?

If he is showing any signs of distress such as panting, pacing, whining etc., then you should call an emergency vet near you.

I am not a vet but a vet tech so the best I can do is direct you to call a vet and ask them locally what you can do. That way you can answer the questions I asked and tell them the details.