Accounts for users under 13 years old have certain restrictions to protect their privacy. For example, under-13-year-old users are unable to connect their accounts to College Board.
That said, it could be that you have a child who is no longer under 13, but their account is still set as if they were. As a parent, you can change their birthdate and allow them to connect their account to College Board.
The simplest way to do that is to log into your parent account and go to your Parent dashboard. You can reach your Parent Dashboard by clicking on your name in the top right corner of the page and selecting it from the drop-down menu.
In it, you should see a list of all your children. Next to their name, you may find the option to Edit settings. Click on it to proceed.
Note: if you do not see the Edit settings option next to your child's name, this means that your child's account is no longer an under-13 account. Therefore, they should be able to connect to College Board already.
Once you are on your child's Settings page, you can set their correct birthdate.