Any food which he likes can be substituted for milk. It can be fruits, normal daily food, or even some fast food, but made at home. U may use a few alternatives like buttermilk (chaach) or plain mattha All Milk products like paneer,curd etc are ok, the Only issue is plain milk per se. U may try to replace it with juices as well, if nothing else works

Avoid giving milk

Avoid giving milk. But can give milk products of his choice. Make it yummy by adding little salt and jeera powder / pepper. Paneer curd chaach whatever he likes. The rest of the food and fruits can be given. Be consistent and wait. After 6-8 months gradually we can introduce milk in a small quantity. Most of the cow milk allergies resolve over time.