Hi! Sorry to hear that you’re dealing with this situation. Unfortunately, Microsoft Support cannot change the date of birth on the account or convert it from a child account to an adult account on your behalf. For safety and privacy reasons, this can only be managed by the account owner, and if the account was created as a child account, this usually requires help from a parent as an organizer in the Microsoft Family group. In the same way, only the account owner can request deletion of a Microsoft account; Support cannot delete it for you.
If you do not want to continue using that Microsoft account, one option you could try is switching your PC from that Microsoft account to a local account instead, so you can keep using the device without losing the data already stored on the computer. After that, you can create or add the correct Microsoft account later and use it normally. If you still want to remove the incorrect Microsoft account completely, that process would need to be started by signing in to the account itself and following the account closure steps.