How do I refile my child tax credit for 2020?

What?   Re-file for the child tax credit for 2020?   Are you sure that is what the letter says?   If you filed a 2020 tax return that claimed a qualifying child under the age of 17, the child tax credit was added automatically to your 2020 return.   Look at your 2020 Form 1040.   Is there anything on line 19 or line 28?

Are you by chance confusing that letter with letter 6419 that is going out to everyone who received advance child tax credit payments between July and December of 2021?

If your letter is really about 2020, then you can amend your 2020 tax return:

Select your tax year for amending instructions:

• 2020