@jana8  Since you did not e-file a return in 2019, & mailed it in, try using a Zero (0) for your AGI.  The IRS was backlogged processing 2019 mailed in returns that allot of mailed in returns did not get processed until late.   You can request a transcript, it will show your 2019 AGI & check the date when it was processed.

Most taxpayers who have had a PIN before the IRS discontinued it can still use their PIN that was used in 2019.

The second-best place to get your AGI is from the IRS. You can order a free transcript of your return at the IRS Get Transcript site or you can purchase a full copy of your 2019 return. Both versions will include your AGI.  The Online transcript is easy to apply for & in about 15 mins. you have your information.

See the following:

Why the IRS Discontinued the E-file PIN and What That Means for You

Filing your taxes electronically is convenient and stress-free — but cyber-attacks have targeted the security of the Electronic Filing PIN, a unique signature used to file your taxes online. This attack caused the IRS to change its e-filing identification system for the 2018 tax year. Here's what happened, and what it means for e-filing your taxes this year.

How to File Your Taxes Electronically After the Change

While shuttering the e-file PIN program means you can't request a new PIN for the coming tax year, it's still easy to verify your identity and file your taxes online. Here are your options:

1. Use a Self-Selected or Previously Issued PIN: If you've used a self-selected PIN in previous years, you can use the same PIN to file your taxes electronically for the 2020 tax year—in essence, you'll notice no difference. Or, if you've been issued an Identity Protection PIN (IP PIN), you can use that to file your taxes online.
2. Use Your 2019 Tax Return: You can also file your taxes online using your adjusted gross income (AGI) from last year's tax return to verify your identity. If you filed your taxes with TurboTax last year, you can access last year's tax filing to find your AGI. Look on Line 8b of the 2019 Form 1040.