Traditionally, camera swapping involves tapping on the source that you want when you want it. However, if there are two primary angles that you need to use, then you can toggle back and forth between those easily with no extra work!
You can learn how to work Swap Mode by watching the follow video, or follow the steps below!
First, you need to open the Preview Window. Do this by tapping on the icon with the four little squares in the bottom-left corner of the screen.
Your currently-live source should already be in the Live Window. Tap on your second source to add it to the Preview Window.
Next to the word "Sources" is an icon that has two oppositely-facing arrows. Tap on that to highlight and select Swap Mode.
Now, tap on Preview -> Live. The source from the Preview Window will move to the Live Window as usual, but now the image from the Live Window will swap back to the Preview Window.
Keep tapping on Preview -> Live to quickly toggle back-and-forth between the two sources!