jeolp, if you are using the CD/download version of TurboTax, no that you have filed you can override line 14 of the 2020 Form 8606 to show the correct basis. When you transfer this modified file into 2021 TurboTax, the correct basis will then transfer in.
If you are using the online version of TurboTax, wait until after the online version of 2020 TurboTax is taken down. You'll then be able to download the amendment version of 2020 TurboTax and do as I described above. You should then be about to upload your modified file if you want to use online TurboTax to prepare your 2021 tax return.
