Using green screens (chroma keying) is a popular option for videographers to create unique backgrounds for their videos. It is natural for them to want to use green screens for their live videos as well. There is not a way to do green screening from inside the app itself. However, if you have a green screen app on one of your iPhones or iPads, you will be able to set this up for use with Switcher Studio.
We highly recommend the app, VeeScope.
Open the VeeScope app, and position the camera where needed on your subject with the green screen behind them. Next, use iOS screensharing to share your iOS device's screen inside of Switcher Studio as an additional camera source.
The complete process will be Green Screen App (iOS device) -> iOS Screensharing -> Switcher Studio.
Here is a guide that will help you set up iOS Screensharing: https://switcherstudio-support.switcherstudio.com/article/168/cast-an-ios-screen-to-switcher-studio.