To resolve the issue with your Microsoft account being locked due to incorrect birthdate settings, you will need to contact Microsoft support directly. Since you cannot access the parent account to make changes, they are the best resource to help you unlock your account and correct your birthdate. You can explain your situation to them, and they should be able to assist you in removing the screen time restrictions and updating your account information.
Unfortunately, there is no direct way to change the birthdate or remove screen time restrictions without parental consent or support from Microsoft.
References:
- How do I stop supervising my child in Family Link? - Microsoft Q&A
- Troubleshoot sign-in issues and account access problems
- I have issue signing in to my microsoft office account. - Microsoft Q&A
- Legal Name - Microsoft Q&A
- account unavilable - Microsoft Q&A
- Manage emergency access accounts in Microsoft Entra ID