Reattaching removable flash (Stubben switch)

I have a Stubben switch bridle (that I adore). I removed the flash last year for a lease horse; now I have my own horse (hooray!) and am using the flash again. I have struggled to reattach it - the actual shoving it back in the noseband was tricky, and today it fell out during tack up.

Does anyone have any tricks/suggestions? I adore this bridle (and this feature) and want to mske it work.