Did you buy the 2023 program? You need to download the .tax2023 file which you can open in the Desktop program.
How to finish a return you started online
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/01/26322
If you can't get the side menus to open up to access the prior year..... You need to start entering some basic Personal Info in 2023 for the side menu to open up. Just continue a little ways into 2023.
After you get the program installed the first thing to do before you open the .tax file is to update the program and install any state programs you had. Then open your file. So you first might need to start a fake return to be able to download the state program (go to FILE - NEW).
You have to print and mail prior year returns. When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return. Don’t forget state.
Then when you do file 2024 enter 0 for the 2023 AGI since you are filing 2023 late.