Hi and welcome to YT! So glad you are taking good care of this sweet boy
I would try plain boiled chicken, white rice, apples ( cut into small pieces no skin) plain yogurt and add a little bit of kibble. That way he is getting food he may be used to but it's better for him. If he isn't eating the dry kibble mix the ingredients above with wet. His teeth might be bothering him. What's his name? would love to see pics