To follow-up on the comments from @DanaB27, you may need to amend to the extent that you did not properly account for any non-deductible traditional IRA contributions. Your amended return may not change your tax liability for the prior year to the extent you did not receive a deduction for your IRA contribution (hence the term, "non-deductible IRA contribution).
Yes, your traditional IRA basis is the total non-deductible contributions you made to that account. Your traditional IRA basis would not include any gains, dividends, or interest. In other words, your basis includes only your after-tax money dollars contributed to the IRA for which you were not able to deduct such amount on your return. When you rolled your traditional IRA into the Roth IRA, you would need to know your basis in the traditional IRA so that your basis, as represented by your non-deductible contributions, is not taxed twice.
To amend your 2020 return, and assuming you filed through TurboTax in 2020 and used TurboTax online, log into your current account. Click on Tax Home, left margin, and scroll down the page to Your tax return & documents. Click on the drop down arrow on the right to open the menu. Select Amend (change) 2020 return.
@dhuynh44
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