See this TurboTax FAQ on how to find your AGI
You can get free 2019 tax transcript from the IRS
If you filed late last year there is a good chance that the 2019 AGI never was entered into the e-file database. Try using 0 (zero) for the AGI.
If you filed an amended return use the AGI on the first filed tax return.
If it continues to reject then the AGI in the IRS database might be in error. Mail filing is the only option.
Also see: https://www.taxpolicycenter.org/taxvox/are-irs-security-tools-blocking-millions-people-filing-electr...
If the AGI from the originally filed return will not work then use a single zero for the AGI ($1 if you filed a non filer return). If neither of these work then your only options are (1) mail in the return or (2) use a paid tax pro since they don't need to use an AGI to file.