Hello! If you're using SKYBOX Rift version, there's no AirScreen channel. You can just click "DIRECTORY" at the top of the interface to access your local drives.
If you're using SKYBOX Quest version, there's AirScreen channel in the left sidebar.
Please check how you open SKYBOX on your Quest 2. If you enable Oculus Link or use a link cable to connect to your PC, you may use SKYBOX Rift version. If you directly open SKYBOX from app library on Quest 2, you're using the Quest version.
You can also click "Global Settings" to check the version number. The latest Quest version is 1.1.0(548).