You can amend the 2020 return to report the extension payment that was not reported on the original 2020 return ( calling the IRS will not work) but you cannot efile it thru TT ... it has to be mailed in at this late date. Expect the IRS to take 6 months or longer to process that return so if you do choose to apply the refund to the 2021 return then put he 2021 return on extension and make a payment if needed with the extension that reflects the 2020 applied amount.
