We have a similar wooden bottomed cushion although we have not attached the bar. If you lift up the rear seats ,toward the back end you should find a notch on each for the uprights this is where the ends of the wooden bar fit having removed the cabinet (if you have one) it then makes the rear lounge a sort of u shape. We've only used ours once when we had a serious card school going on with all the children and their various significant others,.
Denise