My babys formula was switched today by the doctor and he doesn't like it but has to have it. how can i get him to eat it?

Be patient: This is one of those situations where you need to exercise some patience. Try to introduce it slowly, perhaps alternating with the previous formula he had. There are a couple of really nasty tasting formulas that are intended for very special situations. With the information that you provided, one cannot elaborate anymore.

Insist on it: Some formulas simply taste bad. The key is to "stick to it". After 7-10 takes, she will like it for sure. I tip i can give you, if she "just won't drink it" is to prepare formula as indicated in can, then add plain pedialyte (ie. 2 ounces prepared formula w 2 oz pedialyte). This dilutes the bad flavor a bit so she'll accept it. Then begin taking away pedialyte over 1-2 days.