You don't enter it. Turbo Tax calculates it. For What year? 2020 or 2019?
Your current 2020 AGI is on 1040 line 11. Before filing, You can preview the 1040 or print the whole return
https://ttlc.intuit.com/community/accessing/help/how-do-i-preview-my-turbotax-online-return-before-f...
You need your 2019 AGI on the 1040 line 8b to efile 2020.
