You must amend your 2019 tax return to report this distribution by entering the 2019 Form 1099-R into 2019 TurboTax. You do this separately from your 2020 tax return; it has nothing to do with your 2020 tax return.
https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/00/123845...
