That happened on my Blitz. All I had to do was push the spring into a notch in the sear and then a notch on the frame and push the sear down a few times to make sure it was working correctly. It could be a little different on the KP Frame, but hopefully this helps.
i took the sear and super glued it to the end of a screw. then super glued the head of the screw to the inside of the grip frame then just taped it for extra security. it doesnt look good but it does the job and inside the grip frame anyways so no one can see it.