How can I replace broken plastic gear on Singer touch-tronic?

Singer touch-tronic 2010 memory machine? The plastic gear broke and I cannot move the bar over far enough to slip the new one in place. I loosened up all the other gears so the 2 bars can freely move, but the inside bar which holds the plastic gear still will not slide over far enough. The plastic gear is #383961 rotating hook drive shaft bevel gear. How do I install the new plastic gear?