Squirt a couple shots of WD-40 (it's helpful) in the joint where the column protrudes out from the chair base bottom.
While the base is up-side-down, place 2 or 3 legs (for support) on the work bench edge as close to the column as possible, and with a steel hammer, hammer out the column from the base by hammering on the protruding thin edge of the column with medium hard blows...it will remove. The chair will drop to the floor, so watch your feet! Set the base aside and wipe out any WD-40 residue with a rag.
Then using the wrench and WD-40 or removal tool and WD-40, remove the cylinder from the mechanism attached to the bottom of the chair seat. Wipe out any WD-40 residue.
Installing the COM cylinder
Hand insert the plastic button end of the COM cylinder into the mechanism. Just simply shove it in! Now take the 5 leg base assembly and slip it onto the bottom of the COM.
Turn the chair over and sit in it once or twice to tighten the taper fit.