The drawer (upper or lower, whichever is affected) must be removed for access to replace the prism into the frame.
First photo shows the location of the light pipes on the right side of the control board inside the front of the drawer and the location of the prism in the frame.
Second photo shows the prism orientation. Taped on the outside of the frame for reference but, of course, it goes INSIDE the frame. The nubs on the side of the prism match into the little holes in the frame to anchor it.
Your prism is an updated design with a little tab extension on one end. The prism is supposed to have a slight upward tilt and my guess is yours mounts with the tab at the bottom to insure there's proper tilt. You have a double-drawer unit so you might have a look at the other prism that's in place to check the orientation of the tab.
Be careful when refitting the prism so as to not break off the tab or anchor nubs.
Q
