Unfortunately, you can not assign these to set buttons on your controller, but there is a way you can quickly and easily change items. (twinfinite.net)
When you are on the app, simply tap on the left settings button in the top - left hand corner of your camera screen. (digitaltrends.com)
A two - finger swipe, like on stock, brings down the entire quick settings button selection in one go. (pocket-lint.com)