How do I sign and file

Click on FILE from the left hand menu in TurboTax Online to file your tax return.   You will have the option to file by mail or e-file (recommended).    

You sign and verify by entering your 2023 AGI.  There is no actual signature on an efiled return.

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