How do I find last year's AGI of one person when filing as married?.

 On a  Joint return there is only 1 AGI.   You use the same AGI for each of you.

You need your 2023 AGI to efile 2024. The AGI is on 2023 1040 or 1040SR line 11. If you filed a Joint return you use the same AGI for each spouse.

How to find the AGI.
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947

If you didn't file 2023 or filed it later in the year or mailed it, then try entering 0 for the AGI. If that doesn't work you will have to print and mail your return.

Or request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript

Your 2023 AGI is located within your prior-year tax documents Form 1040, Line 11.

There are a few reasons why your AGI, even if it is correct, it might not work, such as if your 2023 return was processed after April 15th, 2024. In this case you can try putting "0" for the AGI. See the link below for more details and scenarios. If after trying with "0" it keeps getting rejected you will have to paper file your return.

How do I find last year's AGI?