Ah, sorry there, I thought you want to rotate the something to match the Camera.
I didn’t know you are trying to rotate the camera/HMD itself. That’s nothing I would really recommend, but I guess
you need that 
I think you can’t set the Relative Rotation of the Camera, as the Camera follows the HMD.
I found out that you can call “Reset Orientation and Location”, which will set the YAW value.
This means, it simply sets the Relative Rotation YAW of the HMD to the YAW value you put into.
I haven’t checked how to properly rotate the camera with this, but this is basically the thing to FORCE rotate the HMD.
Following Blueprint Code moves the head constantly 20 unity a second around the YAW Axis, while also taking into account that
the Player Moves his head at the same time. So it only adds on the current YAW.
