Chances are that the ball bearing inside the switch mechanism itself has popped out from where it's meant to be.
If you're confident to do so and have some spare time on your hands, take the switch out, place upon a tray on a steady table and let's begin...
Pull off the operating switches - they should pull off quite easily
Undo the screws on the back, then using a small flat blade pop out all the catches you'll see, then (carefully) remove the front plate.
You'll now see the inside of the switch - just a load of bent metal, ball bearings, springs and plastic. Note where each of the plastic operating levers go - they all have their own place!
Now to rebuild the switch, make sure each plastic operating lever has a ball bearing at the bottom, place a spring on top of that, then a ball bearing on top of that again. I guess the switch that controls "move forward" has lost a ball bearing somewhere...
Re-assembly is simply the reverse of removal...
Alteratively for a quick fix, take out the drivers switch and the passenger switch, plug the passenger switch into the drivers loom and move it using that, then put everything back together once you're done. If you're not going to move it again!
Hope that helps..