When did you file 2019? If it was late in the year or you mailed it, try putting in 0 (zero) for the AGI. And see, https://ttlc.intuit.com/community/rejections/help/what-if-i-entered-the-correct-agi-and-i-m-still-getting-an-e-file-reject/00/27031
How to correct the AGI
https://ttlc.intuit.com/community/agi/help/where-do-i-correct-my-agi-in-turbotax-online/00/26311
If you can’t get it to efile you will have to print and mail it.
How to mail a return from the Online version
https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online/00/26258
Be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
For AGI Reject code 031
https://ttlc.intuit.com/community/rejections/help/e-file-reject-ind-031-04-or-ind-032-04-the-agi-or-self-select-pin-from-last-year-doesn-t-match-irs/00/27197
Zero sometimes works, depending on the exact circumstances.
I filed 2019 returns in July.
My concern with "trying" a $0 is that amount is incorrect and just compounds the problem. Really don't want to print and mail.
It's ok to try 0. It won't affect anything. It will either get accepted or reject again. If 0 rejects you will have to print and mail.
The IRS recommends entering a 0 for the 2019 AGI - https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue
E-filing your 2020 tax return: To e-file you will need to enter your AGI from your tax year 2019 tax return. If your 2019 return has not yet been processed, you may enter $ 0 (zero) as your prior year Adjusted Gross Income.