Assuming it's the "Beehive" type tang sight, you've done nothing more than run the staff up a whisker to far, and the little "key" that engages the slot in the sight cylinder body is slightly out of time,...with just the slightest bit of preload on the beehive nut, you should be able to twist the staff a bit, and feel it drop back into the slot.
I'm not going to speak to dismantling that sight. I've had a hockey sock full of em' apart,....and do remember that there's some sort of collet that needs freed up, ...prior to pulling the thing apart.
Get it OFF the rifle, and figure out a gentle way to fixture it in your vice,.... for starters.
GTC
