To change the taxable amount, you will need to enter the amount of the 2019 distribution as basis in the nondeductible contribution screens. This will decrease the taxable amount of the IRA by the 2019 distribution.
We don't have specific information on the income qualifications or procedures for the third stimulus payment because the measure hasn't been passed yet. However, If you had issues receiving your earlier stimulus, then the best way to ensure that you are one of the first to receive any future stimulus payments is to file your 2020 tax return as early as possible and use direct deposit so that the IRS will have your updated information.
You can find the most up to date information from the IRS here, and updates from TurboTax here as they develop.
