To cast programmes to your TV from your mobile app, you must first download the app and pair it with your Better TV device. Find directions on how to pair your mobile app here.
This shows a mobile app that is not connected to a Better TV device:
Tap the cast option to select your set-top-box from the list of devices.
This shows a mobile app that is connected to a Better TV device:
You can now use your mobile app to cast programmes to your Better TV device. Simply navigate to the programme you wish to cast and play it. It will start to load on your set-top box after a few seconds.