...
In the class view, select NEW CLASS to create a new class.
Give the new class the same name, start date, start time and duration of the class you are duplicating and click OK.
4. Upload the presentation only recording to the newly created class
Click the '+' icon in the new class to add content, and select Add video. 
Locate the presentation only video you downloaded earlier and use the dialogue box to upload it.
5. Delete the original class
Click on the trash can icon associated with the original class to delete that class.