Help needed (vulcain cricket content)

Could someone please explain me how should I close the case back of my vulcain cricket? I’m asking because in the interior of the case back there is a pin and I really have no idea what it is doing and where it should seat on the movement. I will post pictures for you to see what I mean

I suppose there is something to do with the alarm function because the only watch I had with the same particularity was a favre leuba alarm.

I’m such a newb… but I guess that’s how we lear 😟

Cheers mate 😀

what does rage little pin do? I know the alarm works perfectly without the case back 👎

i can’t thank you enough for both your advice and explanation. It makes sense 👍