Cannot amend 2020 Return: "Amending a prior year return is not currently supported by IRS Free File Program delivered by TurboTax"

I would like to amend my 2020 tax return as I didn't claim a credit that I was eligible for. But when I click under the 2020 "Amend (change) 2020 return" option, the message says "Amending a prior year return is not currently supported by IRS Free File Program delivered by TurboTax". I used free file because my income was low enough to qualify in 2020. I don't mind paying to file the amendment, but TurboTax website will not let me even access to option to amend the return. What should I do?