Turn the auger to move the chain until the master link is positioned on top of the boom.

Place the smaller, flat end of a 3/16 inch pin punch against the end of the master link pin that previously held the cotter pin.

Hit the larger end of the punch with a heavy hammer to tap the pin out of the master link.

If you are still having trouble, a two-jaw gear puller or in-line pin puller might work better. When using a gear puller, it might be necessary to stabilize the claw side of the puller with some kind of spacer that won't be crushed when you start pushing the pin out. A 3/4 inch socket works well.