I agree with giving it a few days and then seeing if he/she will eat. If not, check your water parameters to make sure they are normal, do a water change, and see if he/she perks up and eats. Some fish will go off food for no reason and then suddenly they will eat again. After a few days, try a different food.
Not sure if this is allowed or not, but there is a guy that I get my fish food from and he is excellent. John Patakos sells fish food and fish really do go crazy for it. It is called plecocaine. He lives in Cleveland, Ohio. He does have an aquabid account. When you go there, you can say that I sent you. He knows me as BabyGirl77 as well as my regular name. He is really great at getting the order to you within a few days to a week.