Okay, this is kind of embarrasing but I've spent 20 minutes trying to work this out.

I can't work out how the microswitch sits in the led holder thingy. The only way it goes together, when you press the button the white thing misses the little red button on the microswitch.
I'm sure I'm being really thick here, but will someone please enlighten me.
Here's a photo to illustrate :
