Did you start before Oct 15? You need to switch to the Desktop program to finish.
Online is now closed. You have to print it out and mail it now. Or finish it and mail.
How to finish a prior year online return
If you paid for the Online version you can ask support to give you the Desktop download. Contact Customer Service 5am-5pm Pacific M-F
The Desktop program you install from a CD or download. When you worked on your return was there a black menu bar on the left side or a blue menu line across the top?
Start the program and go up to File-Open. Did you save your file? Are you on Windows or Mac? The Windows program does not automatically save.
If you used the Windows Desktop program you need the file ending in .tax2019 to open in it. The tax files (and PDF files) should be in your Documents then in a Turbo Tax subfolder. If you can't find them do a search for all files ending in .tax or .tax2019, etc. And check the Recycle Bin. For Windows 10 check the One Drive. Did you make any backups? Like DropBox.
If you don't have the main .tax file you might have one that starts with a Tilde sign ~ like "~your name.tax2019". That file is if your computer crashes or your real file gets lost or deleted or corrupt so you can restore it.
Find your Tax file in Windows