My birthday is wrong how do I change it

See this instructions on how to change your birthdate.

From this apple support article: Update the birth date associated with your Apple ID - Apple Support

If you need to change the birth date for someone below age 13, contact Apple Support.*

1. Sign in to appleid.apple.com.
2. Select Personal Information, then choose Birthday. 
3. Update your birth date and click Save. If you're changing a birth date for a child, learn what to do. 

Depending on how you created your Apple ID, you might be required to provide additional information or change your Apple ID username from a mobile phone number to an email address.

On your iPhone, iPad, or iPod touch

1. Go to Settings > [your name].
2. Tap Name, Phone Numbers, Email. You might need to enter your Apple ID password.
3. Tap Change Birthday or Birthday. 
4. Update your birth date, then tap Done. If you're changing a birth date for a child, learn what to do. 

To change a birth date to any age below 13,* you must be a member of a Family Sharing group, and your family organizer must approve the change. After you change a birth date to any age below 13, you can't edit it.* Learn more about Family Sharing. 

1. Update the birth date.
2. Follow the onscreen steps to send an email request to your family organizer.
3. Your family organizer will get an email with instructions to approve the request. 

If you still cannot change your birthdate, Contact - Official Apple Support to get further support on this issue.