Please see the following TurboTax FAQ:
You can find your 2018 Adjusted Gross Income (AGI) by:
Check these items as well to ensure you have the correct number. If you:
Time-saving Tip: If what you entered is correct and you continue to get a reject, you won't be able to e-file. There's probably a data mismatch at the government, or some other situation beyond your control that prevents your return from being e-filed. In this case, your only option would be to print and mail in your return.
This article will give you instruction on how to print and mail your return.
The steps for accessing last year's AGI can be found here @Campcon519.