When on a video call, you can decide at anytime if you want the other user to see what your front camera or back camera is watching. This allows you to switch while on a conversation between different views.
In order to do so, you will find a little circle formed by two arrows on your screen during the video call. Pressing on this icon lets you easily switch between the front and back camera. If you don't see any icon on the screen while on the video call, gently press anywhere on the screen for the different icons to appear.