First of all, insist on not giving any other food or snacks. Cut off the idea that he has other food. In particular, human food is not suitable for dogs, and the salt content of human taste greatly exceeds the intake required by dogs.
Secondly, send him food on time. Give him 15 minutes to eat. Take it away immediately, and don't give any food at other times. Although you won't eat this time, just give him something to eat. Let her know that you can't eat without eating. But drinking water should be sufficient. If your dog is lazy and eats only once every three to five days, just be hungry for 5 to 7 days and then start feeding on time.
A friend of mine didn't want to be hungry at first, and he thought about changing recipes for dogs all day. In the end, the dog didn't even eat her cooking. She was brutally hungry for five days. On the fifth day, she ate everything in the basin. No more picky eaters.
Dogs are domesticated from lack of food, and it is no problem to be hungry for a week or ten days. But there must be enough drinking water. Beware of rummaging when you go out. So be sure to wear a collar when you go out. There is also the need to unify the position with the family. Don't be a dog that can't bear to watch you. You know, one biscuit is enough for the dog to endure hunger for a few days, and wait for the next one.