Move Message Pane (from bottom of screen) to Message List Pane

With the latest update the Message pane showed up in the message pane list. So when I open up the app in the Message Pane List shows Subject, Correspondents, Date, and the message pane (message contents). I've somehow removed the message pane from showing up on the right side. When I change the view to show the message pane it shows up underneath the Message Pane List. How do I get it back over to the right side so it shows the show the message without having to open each individually?