What you need is your 2019 AGI from line 8b of your 2019 Form 1040 in order to e-file a 2020 return.
Where do I find my AGI?
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/00/27010/message-id/746
Your 2019 tax return shows your 2019 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040 line 8b
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 2019
If entering the amount from your 2019 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