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