Help!!!!!!!!! Trailblazer Ss Gear Shift

I AM A UNITED STATES MARINE AND I'M TRYING TO GET SOME MAINTENANCE DONE ON OUR RECRUTING TOOL. IT'S A 2006 TRAILBLAZER SS. mY PROBLEM IS THE GEAR SHIFT. IT'S BEEN WORKING FINE SINCE WE'VE HAD IT UNTIL NOW. i GOT IN STARTED HER UP AND WHEN I TRIED TO PUT HER IN DRIVE, I NOTICED SHE WAS STUCK. THE GEAR SHIFT WOULD NOT MOVE AT ALL. I DON'T KNOW WHAT TO DO ABOUT IT. I ASKED MY SSGT WHAT IT COULD BE AND HE SAID THAT IT WAS THE "NEUTRAL SAFETY SWITCH" THAT IS NOT RESPONDING... HOW DO I FIX THIS?????