I filled my return for 2020, and after that I added contribution of $6000 to my Trad IRA, which I will be rolling over to Roth IRA for year 2020. What tax form I need?

[DanaB27]

The $6,000 nondeductible traditional IRA contribution for 2020 will have to be reported on Form 8606. Please see How do I amend my 2019 return? If your tax return doesn't change then you can send Form 8606 by itself. Sign Form 8606 and send it to the IRS at the same time and place you would otherwise file Form 1040, 1040-SR, or 1040-NR. Be sure to include your address on page 1 of the form and your signature and the date on page 2 of the form.

To enter the nondeductible contribution to the traditional IRA on you 2020 return to create Form 8606:

1. Login to your TurboTax Account 
2. Click on "Search" on the top right and type “IRA contributions”
3. Click on “Jump to IRA contributions"
4. Select “traditional IRA”
5. Answer “No” to “Is This a Repayment of a Retirement Distribution?”
6. Enter the amount you contributed
7. Answer “No” to the recharacterized question on the “Did You Change Your Mind?” screen
8. Answer the next questions until you get to “Any Nondeductible Contributions to Your IRA?” and select “Yes” if you had a nondeductible contributions before this tax year.
9. If you had a basis in the Traditional IRA before then enter the amount.
10. On the “Choose Not to Deduct IRA Contributions” screen choose “Yes, make part of my IRA contribution nondeductible” and enter the amount.

Next year on the 2021 tax return to enter the 1099-R to report the conversion to Roth IRA: 

1. Login to your TurboTax Account 
2. Click on "Search" on the top right and type “1099-R”
3. Click on “Jump to 1099-R”
4. Click "Continue" and enter the information from your 1099-R
5. Answer questions until you get to “Tell us if you moved the money through a rollover or conversion” and choose “I converted some or all of it to a Roth IRA”
6. On the "Your 1099-R Entries" screen click "continue"
7. Answer "yes" to "Any nondeductible Contributions to your IRA?" since you had any nondeductible contributions in prior years.
8. Answer the questions about the basis and value