You must enter your $6,000 Roth IRA contribution for 2020 under Deductions & Credits -> Retirement and Investments -> Traditional and Roth IRA Contributions. TurboTax will automatically add this amount to your contribution basis.
To enter any contribution basis from years prior to 2020, click the Continue button on the Your 1099-R Entries page to reach the questions about your Roth IRA contribution and conversion basis.
