You use the same AGI on the joint return to efile.
You need your 2020 AGI on the 1040 line 11 to efile 2021.
How to find last year's AGI
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/00/25947
IRS how to find the AGI
https://www.irs.gov/individuals/electronic-filing-pin-request
Or You can request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript
