How do I enter the correct AGI for my son's 2017 tax return if he didn't file a return in 2017?

[JakailaLO]

If you didn't file a 2017 tax return with the IRS, just tell us you didn’t file last year when we ask you. But if you’ve already entered a number for your AGI, manually enter 0 instead. https://ttlc.intuit.com/replies/4231698

Also, If your income tax return was rejected, the government is simply asking you to correct some of the information in your documentation and resubmit. 

For additional information on how to resolve a rejected income tax return, please refer to this Turbo Tax FAQ: https://ttlc.intuit.com/replies/3302275