Here is a simple tutorial on how to setup your VR headset for playing passthrough videos.
If you have DeoVR player (it's free) then just follow the screenshots attached.
Otherwise, follow these steps on your VR player:
Enable passthrough option on your VR player (some might not have this feature);
Set the pure green as the chromakey color;
Maximize "saturation" value;
Maximize "brightness" value;
Set "range" to a medium value (before small and thin details disappear, like strands of hair); and
Set "falloff" to your liking to remove eventual green edges.
PS: big thanks to Gabriel Mühle for the screenshots!