My son has newly received his SSN in July 2019 but I've forgot to update his ITIN into SSN in Tax filing for 2019 in 2020, so we didn't get child tax credit for him.

When I fill 1040x in TurboTax, I can update my son's SSN but it is automatically set him to be invalid for child tax credit. I cannot change it. How can I fix this?