Backdoor Roth IRA conversion - IRA basis

Hi, 

I have a question about how to correct my IRA basis. Here is the backstory of my situation:

 

In July 2020 I made a $6,000 contribution to my Traditional IRA account for year 2019 and another $6,000 contribution for 2020. When I filed Form 8606 for tax year 2020, it asked me to “Enter your nondeductible contributions to traditional IRAs for 2020, including those made for 2020 from January 1, 2021, through April 15, 2021.” Based on this, I put down $6,000 on line 1. 

 

In early 2021 I contributed $6000 (for year 2021) to my Traditional IRA account and later that year I transferred $18,000 (nondeductible contributions for 2019,2020,2021) plus all earnings in that account to a Roth IRA, as part of a backdoor Roth IRA conversion.  When trying to input the conversion in TT , it is asking for my Basis thru Dec 31, 2020. It technically should be $12,000, but it's saying it is different than what I entered on Form 8606 in 2020 which was $6,000.

 

Question:

Since I contributed $6,000 (2019 contribution) to my Traditional IRA in 2020, does that mean I have to fill out Form 8606 for 2019? Or would this be amended to my 2020 tax return? And if so, do I submit my 2021 tax forms with the IRA basis that I think should be correct ($12,000) and explain I'm amending a previous tax return? 

 

Thank you. 

 

- Jay