Put the pneumatic lift in its sleeve and tuck it into a corner of the box.
Lay the 5-star base down into the box (upside-down)
Lay the extra square of cardboard over the chair base.
Put the seat into its plastic bag and place it in on top of the cardboard as close to one corner as possible.
Place the back rest into its plastic bag and put it in the opposite corner with the J-bar pointing downward into the box.
Close the lid of the box.