After you file

Not quite sure what you are trying to do.  Do you still need to file a 2018 tax return?    Or are you trying to e-file 2019 and you want your 2018 AGI so that you can enter it?   Actually, your 2018 AGI is not on your W-2's if that is your issue.

First---if you still need to file a 2018 return:

Online preparation and e-filing for 2018 is permanently closed.

To file a return for a prior tax year

If you need to prepare a return for 2016, 2017, or 2018 you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

Remember to prepare your state return as well—if you live in a state that has a state income tax.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.

Note:  The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac.  It cannot be used on a mobile device.

If you are getting a refund, there is not a penalty for filing past the deadline.  If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.

https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return

Or---if the reason you are concerned about your 2018 income is that you are trying to e-file 2019's return:

https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947

https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/270...

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: 

https://www.irs.gov/individuals/get-transcript

Note: If you filed late or amended your return, your correct 2018 AGI may not be in the system.

https://ttlc.intuit.com/questions/1944348-how-do-i-print-and-mail-my-return-in-turbotax-online

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.

https://ttlc.intuit.com/questions/3415597-what-if-i-entered-the-correct-agi-and-i-m-still-getting-an...