Pull both the locking levers on the rear of the chair in the horizontal position. This is the position the levers are in when removing the chair back.
Place the chair back over the chair arms as if the back were folded forward over the chair.
Lift the chair back at a slight angle and align the brackets on the chair back with the brackets on the rear of the chair toward the inside of each arm.
Push the chair back all the way down, engaging the brackets on each side. Twist the chair back from side to side to ensure that the chair brackets are engaged. The side of the chair back should stay in place.
Press the two locking levers down with a flat-head screwdriver. When the brackets are engaged properly, the levers offer some resistance but will fold flush to the back of the chair.