Quoted from Manny65:
I assume you mean the actuator arm (the metal strip that the ball makes contact with) has come off the black plastic knob on the switch body, that the actuator arm pivots on. In this case unscrew the switch off the wireform so that it is easy to handle, the actuator arm will have 2 holes that clip onto those knobs on the switch (1 on either side of the switch). If that area of the actuator arm has been stretched you may need to press the metal sides slightly together so that it doesn't pop off the knobs on the switch. If the knob has been completely worn down and won't hold the actuator arm in place then you'll need a new switch. Once you have clipped the arm back into place, you should be able to press the arm and hear the switch click. Then just screw the switch back into place (note that the switch will need to be positioned such that a ball passing by will trigger the switch but still allow the ball to continue on down the wireform).
Thanks so much for all the advice and help with the lingo! I took it apart and was able to click it back into place. Best, G