So here's what I did (or am doing):
Log into turbotax and scroll down on the main window to Your tax returns & Documents and pull down the menu to select the 2019 year.
Click Amend (Change) 2019 year.
Under Deductions and Credits there is a Traditional and Roth IRA Contributions - go there and adjust the traditional contributions to the right number and there is a question how much was contributed in 2020 to the 2019 contribution limit so make sure that is right.
Go through all the checks and at the end you’ll get a new TaxReturn.pdf with an updated 8606 form that shows the new numbers and has the additional funds as a Basis for 2019 and prior years listed on link 14.
I printed the pages w/ the updated 8606 form only, added the address and signature/date.
Send that to the 1040x address for my state from here: https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment
Or I could have just directly filled out a new 8606 form here - https://www.irs.gov/pub/irs-prior/f8606--2019.pdf
and sent that in via mail.
Back to 2020 turbotax return, on income under the Retirement 1099-R reporting information, Edit that section and go through all the data again. When I got to the question that says :
Any Nondeductible Contributions to xxxxxxxx's IRA?
I checked yes I made and tracked nondeductible contributions to my IRA.
On the next page "Let's Find Your IRA Basis" adjust the basis up to the corrected amount from the new 8606 form (the Dec 31, 2019 date on that question was throwing me off but I think it means the basis from the 2019 tax return form 8606.
That fixed my taxes owed number.
I'll check my 2020 8606 form at the end to make sure it is correct and not going to double count anything but this looks right so far.
