The screen mirroring remote lets you remotely view your computer screen on your phone. Note that it is currently only available for Windows and Mac on the computer side, and Android and iOS on the phone side. We're adding support for other platforms as well!
Make sure you have the latest version of the app and server.
If it isn't in the main list, press the "+" button in the remotes list. It's the big green button on Android, or the button near the bottom on iOS. Then make sure "Screen (Preview)" is selected.
If you can't find the Screen remote, then make sure your platform is supported, and that you have the latest version of the app and server. See above for a list of supported platforms.