dont worry too much tho, the electronics in your axe should still be 100% fine, that is just a knob for cosmetic and practical purposes.

Head down a guitar store and buy a new one, you may need to replace all of them if you want all your knobs to look the same...that's all there is too it.

If it has a small screw on the side of it,just slide it back on to the pot and fasten it with the screw