Did you use the Backup/Restore option within ProSeries to copy your client files? 

If so, open PS2019 and use File > Client File Maint > Restore and choose the folder or device that contains the client files.

If you just have copies you saved using Windows, I dont think you can use Restore.  Youd just have to copy the files into the 19Data folder, then use the Homebase Database Maintenance within Proseries to update Homebase.