FAQ: How do I find last year's AGI?
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/00/25947
If you used Online TurboTax last year, log in, and at the Tax Home scroll down to "Your Tax Returns & Documents." Expand that section and choose tax year 2018. Then look for a link "Download/print the PDF" or "View adjusted gross income (AGI.)"
If you're not able to find the 2018 online return in that same account you're using for 2019, we can tell you how to look for multiple accounts.