Took delivery of a Headplay HD FPV headset, and not along after, took it apart.
As you do!
To help with splitting the two halves, hold the switch panel down with a finger or thumb whilst you separate the halves:
Inside – you can see the slot where the fresnel lens sits, halfway back towards the rear:
If you haven’t taken yours apart yet, something to be aware of when re-assembling:
Watch out for the wires, and make sure you don’t pinch the wires with the screw post on the other shell half.
The manufacturer really should have contained the push button module wiring loom inside a length of flexible “spaghetti tube” to reduce any chance of wiring damage.
Be careful, when screwing back up again!