In your version it is under Federal. You don't enter the missing amounts. You enter what you actually received for each round in boxes 1 & 2. If you did not get one you enter a 0. Then Turbo Tax calculates if you qualify for more and puts it on 1040 line 30.
When you go through the federal review tab it will ask how much you got if any. Enter a 0 in the box if you didn't get one. Or to enter your stimulus payment in TurboTax, type "stimulus" (without the quotes) in the Search box, then click the link that says "Jump to stimulus."
After you have entered your tax information and are ready for the Federal Review, it will be the first question.
If you are trying to trigger it, you can go to Other Situations, answer any questions and click Done. The next automatic selection is Federal Review and it will ask about payments received.
