What to do when a rubber dome is broken off?

I mean the nipple-like part that I circled on this image (not mine, edited stock image)

. I lifted off the key cap to clean it, and somehow the nipple-like part was broken off from the rubber layer. I placed the nipple-like part at the centre as you see the image above, and put the key cap back. The key is working but is not springly any more.

It seems that opening this keyboard and replacing the entire rubber layer is nearly impossible (all glued together). The only way I could think of is using some kind of glue to attach the nipple-like thing on the transparent film on which a spiral shape circuit is printed, but I am not sure if it would stick to it (because the bottom of the nipple-like thing is hollow). Throwing away the whole keyboard just because that small silicon nipple is broken off seems to be a waste of resources. What is the best way?