Ok so now I need help

My baby had been sick and was not eating anything! I tried Caesar bc I was desperate and now that is all he will eat! My vet wanted me to wait to change his food (kibble) bc he was new to me and very tiny but now I don't know what to do. He will not eat any kibble. I've tried to mix it and he won't have it. How do I get him off Caesar (which I know is junk) and on to dry kibble again. He is one pound and he is controlling me like he is a weight-lifter

I have to be really careful bc I don't want him to get hypoglycemia again.