It's really hard to explain how to fix it. The trick is to rotate the joystick back to where it belongs while pulling it up or pushing it down, slightly. Take the cap off the joystick, and the flat side of the metal should be facing your left hand. Then you have to work with it until it pops back into it's socket.
I've had to do it 3 times, and it always takes me 45 minutes or more to do it. You should feel a slight click when it goes back, and the joystick will be springy again. It's a real pain in the ass to do.