My dependent claimed independent on the non-filer tax form in 2020 for a stimulus check. What form do they need to fill out to correct this so we can get our refund?

We filed a paper return because of this, including a form the kid filled out, but it has still not gotten processed. The IRS tax advocates want us to send them our documents again so they can expedite our refund, but of course the kid didn't make a copy of their form and they don't remember which form it was. I can't find any information on how to amend the nonfiler form anywhere.