GearVR 2016-2017 40mm fan mount. I used a 40x10mm fan, but 40x20mm should work as well. One part is taped to Gear VR case and acts as a socket for the second part - the fan mount. For Galaxy S6 tape the socket as in Picture 1. For other phones you will need to find the spot that heats up the most and place the fan there.
As shown in Picture 3, don't tape over the circled areas as they are moving when adjusting the focus.
The uploaded STL's are improved version, so they might differ slightly from the photos.