He is just a baby and needs to be fed. If you are sure of the nest, putting him back in would be best. Much better if raised by the parents, as they teach him what he needs to know to survive. If you can't do that, then you will need to hand feed him or he will starve. He doesn't know how to eat on his own. If you can either get frozen peas that you would defrost and warm in warm water, or cook fresh peas til they are soft, then cool til just warm not hot, this is how you would do that.
If you need to feed peas to a pigeon, hold the bird on your lap and against your body. This gives you more control. Reach from behind his head with one hand and grasp his beak on either side. Now use your free hand to open the beak, and put a pea in, then push it to the back of his throat and over his tongue. Let him close his beak and swallow. Then do another. It gets easier with practice, and the bird also gets more used to it, and won't fight as much. If you can't handle the bird, then use the sleeve cut off a t-shirt, slip it over his head and onto his body, with his head sticking out. This will stop him from being able to fight you so much. Just don't make it tight around his crop area. It helps if you have him facing your right side if you are right handed.
