Thanks for you suggestions.
I removed the cable and the spade connectors from the switch. That gave me just enough slack to slide the plastic hadle far enough to get the loose bit out. I could then slide it into its correct place. I kept the hanle pointing down so it didnít slide out again and slid the two bits together. I put the screw back in to stop the retainer falling out. Next I reconnected the spade connectors and attached the power cable. Holding the handle with the top down I then took out the screw, closed up the handle, slid the two parts together and tightened the screw. It worked, bingo.