I assume you mean the center pin
schematic.
That is a fitted part, so you will need to know how to fit it for length.
You just basically disassemble the cylinder.
1. Unload revover
2. remove yoke screw and remove yoke and cylinder from the revolver, take care not to scratch the frame
3. I install 3 fired casings in the cylinder to prevent shearing the locator pins
4. Turn the extractor rod in the correct direction. It will probably be a left hand thread unless your revolver is really old. Don't use vise grips on the knurled end.
5. Unscrew it all the way
Everything will just come apart now.