If you filed a tax return last year, you will find your AGI on your previous years tax return. You can find multiple ways to retrieve that information below.
https://ttlc.intuit.com/questions/1900840-how-do-i-find-last-year-s-agi
If you did not file last year, you will need to follow the instructions below.
https://ttlc.intuit.com/replies/4231698
