On Windows and Mac (Sookasa version 3.X.X):
From Windows Explorer or Mac Finder, simply drag the folder and drop it into any location outside of Sookasa when the Sookasa app is running. The contents of your folder will be automatically decrypted.
If you've moved the folders out of Sookasa when the Sookasa app was not running, simply start the Sookasa app, right-click on the folder and select 'Decrypt'.
On Windows (Sookasa version 2.X.X):
Right-click the folder and select 'Decrypt folder' from the menu.