See this TurboTax support FAQ for entering the 2017 AGI - https://ttlc.intuit.com/questions/2551840-where-do-i-correct-my-2017-agi-in-turbotax-online
When you sign onto your online account and land on the Tax Home page instead of the Take me to my return page, follow this procedure -
When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. See screenshot
This will take you back to the 2018 online tax return.
