Yes a payment you got in January or February 2021 is an Advance and based on your 2020 return.Enter the second Stimulus payment on your 2020 return now.The year you got it doesn't matter. If you don't report it Turbo Tax will give it to you again, which would be wrong and double.The Stimulus entry screen says the second one is between Dec 2020 and Jan 2021 so you should include any payments you received in January and February.
