How do I change my birthday my dad put it in wrong by accident

Read this support article about how to update the birth date associated with an Apple ID: Update the birth date associated with your Apple ID - Apple Support

There's different ways to change the age on an account depending upon the age of the person, their target age, and the country's age definition of "child". I do not assume that just because you said "dad" that that means you are a child by Apple's definition.