Unscrew the top of the string cartridge. The spring will push it up enough to remove the cartridge.
On top of this you will see two small holes about 1/2 inch apart.
From your refill batch pull and cut about 10 feet and fold in in half. The two ends are to be put into those two small holes on the top of the cartridge. Pull through and you will have two five foot sections. Wind the cartridge clockwise to wrap iup the string keeping the pair as close together as possible.
When you have about 10 inches left string each piece into the outer holes of the top of the part where the cartridge was seated (this is where you normally see the string line). Be careful to seat the cartridge back in the opening (don't for get the spring) making sure the string will freely feed when the cartridge reel turns during bumping. (don't let the line get under the cartridge when you reinsert it)
Seafari Sam, December 2010