You will need to have the .tax2019 file on your computer. If you used the Desktop program last year here’s How to transfer into the Online version, expand the blue link if you used the CD/download last year........
If you already started an online return you will have to clear it and start over to transfer. How to clear and start over
If you used the Desktop program before you may not like the online version. It has less features and no Forms Mode. You can only do 1 return. Your return is only saved online so be sure to save both the .tax2020 data file and the pdf file to your computer when you are done. In case you need to amend in the future or if you need a copy to get a loan or something. You might not be able to access your online return when you need a copy.
You need to use the *.tax2019 data file from last year to transfer into 2020 Online TurboTax. Do you have a copy of the *.tax2019 data file? If so, we can tell you how to transfer it into Online TurboTax.
I see VolvoGirl already provided you the method in her comment above.