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 filed your 2018 return with Online TurboTax, are you using a different account for a 2019 online return? If so, we may be able to help you locate the account with the 2018 return.
