You cannot open (or work on) a 2019 tax return using a TurboTax online program.
If you prepared a 2019 return with the online version of TurboTax but did not complete and file it, you cannot open it and continue working on it. TurboTax online programs only work with the current tax year (2020).
You will need to use a desktop version of TurboTax to finish your 2019 return. See How do I prepare a prior year tax return?
