Where do I enter my AGI from last year

1. From the menu on the left, select File (tap in the upper-left corner to expand the menu on mobile devices). This will put you on the [Name], just X more steps and we'll file your returns screen.
2. Go to Step 3 (if needed, revisit Steps 1 and/or 2 to activate Step 3).
3. Proceed, and make sure you've selected the option I want to e-file.
4. Continue through the screens, and soon you'll see the place to enter your 2017 AGI.
5. Keep going until you’ve re-transmitted your return.

I am on the online version free

The answer was for the online editions.  Are you not accessing the 2018 online tax return?