Depending on what you are broadcasting you might want to use either portrait mode or landscape view. All you need to do to activate it is rotate your device!
If your hearts and comments are not rotating when switching to landscape, make sure your device's orientation has been turned off and the screen is in landscape mode before you go live.
If you know you want to upload your broadcast to another platform (like YouTube or Instagram), make sure you start your broadcast in the mode you want it to be and keep it that way.
Unfortunately, the Samsung G900 and G800 families may not correctly manage landscape due to manufacturer constraints.