If you just purchased the 2020 program, the only thing it will do with a 2019 tax file is import it to get a Headstart on your 2020 return.
If you have purchased the 2019 program and both the 2019 and 2020 programs are installed on your Mac, then double clicking a 2019 file will by default open the 2020 program to start a new return. Instead, you need to open the 2019 program first and then locate your tax return with the File...Open command.
