"Adjusted Gross Income", its the value shown an 1040 line 8b.
AGI - Adjusted Gross Income
See this website - https://www.investopedia.com/terms/a/agi.asp
For your 2018 AGI it is found on the 2018 Federal tax return Form 1040 Line 7
If you did not file a 2018 tax return then enter a 0 (zero) for the 2018 AGI