If this is for the stimulus checks then there is nothing you can do to change a prior year return to generate the credit ... the only fix now is to file a 2020 return to get any stimulus money you are eligible for that you did not get in advance.
If you have not received your payment by January 27, 2021 you will claim the credit by answering the 2 questions about the stimulus payments that will appear at the end of the TurboTax interview.
The questions are in the section Federal Review.
Once the information is entered you will see your refund increase or balance due decrease, and TurboTax will enter the amount of the credit on Line 30 of Form 1040 for you.
