Take a look at this:
Open the media app. Open menu, select explore. Navigate to your folder. From within the folder, you should be able to open the menu and then select play folder. If you are one level above and scroll to highlight the folder (do not open), you should have a menu item for play subfolder. If because of a different OS you do not see it exactly as I do, you should see the same general capability, I believe, and so experiment.