I'm sorry nobody answered before now Susie. I didn't get the usual notification that someone posted. Sorry

First, the decorative cap is an original part of your car. The installer removed it from the end of the original wiper arm and snapped it onto the end button of your cruise switch (the part that flew off). You can, and should, remove the decorative cap so you can put it on the new switch. A razor blade is best, as you can insert the thin blade under the lip of the cap and pry it off.
But on to your more serious problem... the button flying off the switch. You basically need a new switch. It is covered under warranty if you bought the kit < 2 years ago (in which case please contact your retailer/installer), otherwise a new switch can be purchased from SmartieParts.com
here. Before buying one though, I recommend contacting Steven at SmartieParts and perhaps checking if you can get just the button instead of the whole switch... it may save you the headache of having to re-run the switch cable. Just a thought.