Many a times due to weather change, dogs lose their appetite. You can connect with a veterinarian to understand if your pup is well and is not suffering from any gastric problems.
In case your dog is a fussy eater, you can add boiled chicken / chicken broth / boiled eggs / vegetable stock in the food and give to your pup. There are gravy style food available under different dog food brands. You may try adding them to the food to encourage eating.