Re-assembly of Tefal express pro 2932 steam generator iron?

I've replaced the micro switch in the handle of my Tefal express pro 2932 steam generator iron, but when I first open it, a small spring fell out and now I don't know where to re-fit it. I've looked and tried to fit it in all the what looks like obvious places but it won't stay.

Can someone please advise where this small spring needs to be fitted.

Many thanks