When creating a Facebook Cover Video in the Ripl app we recommend selecting a horizontal post size on the "Create A Post" screen. The designs on the "Customize" step will then only show you templates in the landscape orientation.
You'll want to share the video to your Facebook Page, then go to Facebook on your desktop computer and navigate to your Page. Click "Change Cover" in the upper left corner, then "Choose From Videos" and select the Ripl animation. This blog post may be helpful.