How can I change my daughters birth date on her iPhone?
How would I change my daughters birth date on her phone?
[Re-Titled by Moderator]
How would I change my daughters birth date on her phone?
[Re-Titled by Moderator]
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
The exact procedure you need to use depends upon the age of the daughter and the goal age.
How can I change my daughters birth date on her iPhone?