Oh....you are really confused. Your 2017 AGI has nothing at all to do with e-filing a 2019 tax return.
You cannot e-file a 2018 tax return, so there is no need at all to look for your 2017 AGI. If you prepared a 2018 tax return in 2020 it should have been prepared using 2018 desktop (C/download) software. Since a 2018 return can only be submitted by mail, you did not need to enter anything about your 2017 AGI. You only needed that 2017 AGI in order to e-file a 2018 return before the filing deadline for a 2018 return --which was in October of 2019. E-filing for 2018 is permanently closed.
If you used the current online software for that 2018 W-2 and thought you were preparing a 2018 return, you made a big mistake. The current online software program can only be used for a 2019 return--no other year.
You say you already filed using your 2019 W-2. How did you accomplish that? Did you e-file it? Or did you print, sign and mail it in an envelope? We had better check to see if you really filed it. Post back with details about what you did to file a 2019 tax return--hopefully with ONLY a 2019 W-2.
As for how to correctly file a 2018 tax return using that 2018 W-2:
Online preparation and e-filing for 2016, 2017 and 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/
You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.
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.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
