How long has it been that your dog doesn’t want to eat? If it just started I would advise maybe to try hand feeding him and see if he takes it. If that’s not working then try mixing his food with wet food and you can always warm the wet food a little bit so the smell is stronger. That way the smell is more appetizing for your pet. If that’s not working then something is going on with your pet he might not be feeling well so it’s better to bring him in to get him checked out.