I started my 2018 return onlne but I want to download the software and finish on the computer. how can I move what I entered so far from online to the downloaded return?

Did you already buy the software?   You can purchase 2018 desktop software here:

https://turbotax.intuit.com/personal-taxes/cd-download/

Or did you already pay online?  If so, you'd have to talk to Support to work something out.

The FAQ below tells how to download the *.tax2018 data file you started online to finish it in the desktop software.

NOTE:  If your data file has a state return in it, then you'll need to download the state program into your desktop software before opening the file, or you'll get an error message.  To do that,  you may have to start a fake new return in your software just long enough to download the state program.

FAQ:   How do I switch from TurboTax Online to the TurboTax software?

https://ttlc.intuit.com/replies/3302260