Your 2018 tax return shows your 2018 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040 line 7
If you are using the same TT account that you used last year, you should also be able to find this number in your Tax Home for 2018
If entering the amount from your 2018 tax return does not work, then try entering “0” instead. If that does not work and you still cannot e-file, then print, sign, and mail your tax return.
You can get a free transcript of your past return from the IRS:
Note: If you filed late or amended your return, your correct 2018 AGI may not be in the system.
Note: If you mail your federal return, you will also need to mail your state return. You will not be able to e-file your state return.
it is a good idea to use a mailing service that will track it like UPS or certified mail. Then you will know the IRS received it.
If you used the wrong AGI, your e-file be rejected. When you get the rejection notice, correct it and re-file.