Ignition Key Turned Off. Engine Still Running!

On this snowy Monday, I started my 94 Grand Voyager up but when I turned it off, the engine kept running! The metal around the key seemed to have popped out. Thankfully, when I turned it all the way forward as to start, it seemed to seat back in, then I could turn it off. The auto parts store said it was probably the ignition key cylinder. He said it was a common problem in Caravan/Voyagers. Any help on how to replace it? I'll try!
Any help is greatly appreciated.