If you downloaded the .tax2019 file you need the 2019 program installed to open it.
After you get the program installed the first thing to do before you open your tax return is to update the program and install any state programs you had. You have to first update the federal program before you can download the state program. Go to menu item Online then Check for Updates. If that doesn't work try the manual update. After you update then close the program and reopen it. You might even reboot your computer.
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). Enter some basic information, then go to the state tab and download the state program. Then try to open your existing return, go to FILE - OPEN
