Nothing about any other year's RMD appears on your current year's tax return. TurboTax does not calculate RMDs, it only reports what you tell it. Simply change your year of birth, enter the QCD, then change your year of birth back. Doing so allows you to report the distribution as a QCD and nothing else on your tax return is affected. If by "last year" you mean 2020, if TurboTax asks how much of the distribution was RMD, answer None. If you encounter TurboTax's page that asks if you completed your RMD for the year, simply answer that you did.
