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
Where do I find my AGI?
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
Your 2023 tax return shows your 2022 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040 line 11
If entering the amount from your 2023 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.