There are three ways you can use to locate your AGI:
If you have your last year's tax return, read here: Find your AGI
If you used TurboTax online to file, you can access your account here Login and download a copy of your prior year’s 1040 tax return to find your AGI. Click here for instructions: Prior year's return
If you do not have a copy of the tax forms, you may order a transcript from the IRS. Click here Get Transcript and select "Get Transcript Online " or request a full copy of your past year's tax return. Click here: https://www.irs.gov/forms-pubs/about-form-4506
If remain being rejected, try 0. The last step will be printing out your tax forms and paper file to the IRS. To see explanations, click here: Correct AGI got rejected