If you are completing a 2021 tax return you cannot enter any W-2 other than one for tax year 2021.
You do not need any other AGI to file the 2021 tax return then the 2020 AGI from a 2020 federal tax return Form 1040 Line 11.
If you did not file a 2020 tax return then indicate that in the File section of the program on Step3.
Or enter a 0 (zero) for the 2020 AGI to e-file the 2021 tax return.