If you are talking about the piston type thinghie that removes the knocking sound of the steering rack then any competent (BMW) mechanic would be able to do it. google it to see how easy it is. Did it on mine and the only real issue is how tight to tighten it. Trial and error worked in my case. Jack up the car with the front wheels in the air and tighten it lightly and feel if the steering turns easily. Drive the car and listen for knocks. If it is still knocking slightly tighten it untill it stops knocking and the wheel self centres when driving. Job done.