On a 2019 1040 form your AGI is on line 8b.
You will need your 2019 AGI in order to e-file 2020. If you are about to try to e-file now--forget it. You cannot e-file yet. Tax year 2020 is not over. The IRS will not be accepting returns until the end of January.
Look on line 8b of your 2019 Form 1040 for your 2019 AGI.
To access your prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on 2019 and Click on View adjusted gross income (AGI)