You can activate 'Stream Window' from the 'Streamer Mode' settings in Options.
*SteamVR version only.
The settings for the stream window are as follows:
Spectator Interface:
Enabling this will display the match situation in the stream window.
Screen Tilt Stabilizer:
Enabling this will remove the horizontal tilt of the HMD in the stream window.
Screen Shake Stabilizer:
Corrects minor movements and shakes in the stream window (0: No correction - 100: Maximum).
Camera Offset:
Adjusts the position of the stream window camera forwards and backwards.
Lowering the camera behind the viewpoint position will widen the field of view in the stream window (0: Viewpoint Position - 100: Maximum).