DO NOT alter any of the wiring! That's WRONG.

Remember the two screws under the center of the heated bed, the two that you connected the ends of the Y axis belt to? Loosen that belt and remove those two screws. Flip the belt over so the ends feed off the opposite side of the stepper motor's pulley. Now thread those two screws into the OTHER pair of holes, along with their ends of the belt.

Now it should work just fine.