The stimulus payment was an advance credit for tax year 2020. If you were not eligible to receive the credit based on your 2018 or 2019 tax return, you may be eligible on the 2020 tax return.
There is no offset on the 2020 tax return if you did not receive the stimulus payment in 2020.
You didn't get a Stimulus Check based on your 2018 or 2019 returns? Is your income less in 2020?
The Stimulus Check is really based on your 2020 return we are filing in 2021. So any amount you already got will be reconciled on your 2020 return line 30. If you didn't get a Stimulus Check (and qualify) or you qualify for more it will be added to your 2020 return. But the good news is if they paid you too much they won't take it back.
When you go through the federal review tab it will ask how much you got if any. 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."
See this thread, it has good information and a screen shot
See these 3 IRS questions on reporting it on your 2020 return