Ok ... the programs work exactly the same ... the prior year info is transferred from one year to the other to keep the continuity. All you need to do to switch to the downloaded version is to transfer the 2018 info to the 2019 program ... so if you have not yet downloaded the PDF and .tax2018 file from the online system yet then do so now AND do the same for all the prior year returns since you will lose access to them if you do not use the online version going forward.
If you prepared your 2018 return online, in order for your previous year tax information to transfer into your Desktop software you need to download your 2018 Online return as a .tax2018 file.
https://ttlc.intuit.com/questions/1899645-how-do-i-save-my-2015-turbotax-online-return-as-a-tax-data...
