Start off with lining up the spool pin with the short slot and the long slot on the plier. The short slot is used for pushing the pin out through the long slot.
Line up the plier on the spool pin and squeeze the plier through the pin and the long slot of the plier.
Once the majority of the spool pin has been pushed through the spool, use the push pin on the plier and place it on the short end of the spool pin. Squeeze the plier softly to push the rest of the pin through the spool. Be careful not to squeeze too hard or the pin will fly out.
To reinstall the pin into the spool. Reverse the process and make sure the long end of the pin is lined up on the short slot of the plier and the short end is lined up with the long slot. Squeeze the plier softly to push the pin through where it's even on both sides. If you push the pin too far in, you can turn the pliers over like in step one and line the pin up evenly.