If your filed 2019 tax return already includes 2019 Form 8606 that shows on line 1 the $6,000 nondeductible contribution for 2019, resulting in $6,000 on line 14, there is nothing to amend with regard to your 2019 tax return.
If you began your 2020 tax return by transferring in the tax file that includes this Form 1099-R, TurboTax should have automatically transferred in this $6,000 from line 14 of your 2019 Form 8606 as your basis from years prior to 2020 and included it on 2020 Form 8606 line 2. You can confirm this by clicking the Continue button on the page that lists your 1099-Rs ad proceeding to the page that asks you to enter or confirm your basis carried in from 2019. Your 2020 Form 8606 will also have $6,000 on line 1 from your $6,000 (not $12,000) contribution that you entered as your 2020 contribution. With a $0 year-end balance in traditional IRAs, the taxable amount of the Roth conversion will be the amount in excess of your $12,000 of basis ($2yyy).
You can ignore the code R 2020 Form 1099-R. That recharacterization should have been addressed with an explanation statement included with your 2019 tax return. If no explanation statement was included, be prepared with an explanation statement in case the IRS questions your reporting of a traditional IRA contribution.
