Is there anything you can do for flat feet in dancer?

Usually not. Flat feet may be a problem in ballet, as a foot with a good arch is considered desirable for going on point. Having said that, many professional ballerinas have managed to have fine careers even with flat feet. If a flat foot prevents someone from being a ballerina, then i usually advise them to pick another form of dance.. I do not advise surgery solely to allow someone to dance.
Flat feet. Treatment or intervention is only required if the flat feet are actually interfering with day to day activities including dance. If not flat feet do not need anything done especially if one is born that way.