All you need to do is start a federal tax return using 2020 TurboTax editions. As you progress through the program entering your information and tax data you will get to the Federal Review section of the program.
In that section you will be asked about the stimulus payments received or not received. Any stimulus payment you were eligible to receive but did not receive will be entered on the Federal Tax Return, Form 1040, on line 30 as a tax credit which will be included in your federal tax refund or will reduce any federal taxes owed.
Note - The 2nd stimulus payment has not yet been included in the calculations for the Recovery Rebate Credit due to the IRS not yet finalizing the calculations on the Form 1040. The Form 1040 is scheduled to be updated sometime today, 01/07/2021. Although this is subject to change.
