I assume you have your 2019 returns in ProSeries 2019.

In HomeBase, under File, pick Transfer, Transfer Clients, under Number 1 pick 2019 Form 1040 to 2020 Organizer, pick the clients you want to get organizers, click Transfer.

Now in HomeBase, open Organizer in 2020.   The clients' organizers should be there.

I hope this helps.