Rolex is a Swiss made watch and one of the largest luxury watch companies in the world. To change the crown on a Rolex you must open the case back, remove the current stem and crown, and replace it with a new stem and crown. The stem and crown are attached, so you cannot replace the crown without replacing the stem.
Unscrew the crown until it pops out; the same way you would unscrew the crown to change the time on the watch.
Place the watch case opener in the notches around the outside of the back of the watch case. You have to use a watch case opener made for Rolex watches to open the watch. Once the case opener is in place, twist it and the back will pop open.
Use a mini screwdriver to loosen a tiny screw on the inside of the watch located near the stem. You do not need to unscrew the watch, only loosen it.
Pull the crown straight out. The crown and stem should easily come out.
Insert the new stem into the same location and tighten the tiny screw to its original position.
Close the watch case and twist the watch case opener to secure the back in its locked position.