You have consulted the diagrams which show the exploded view of this and it does not make sense!
Undo the screw at the bottom of the shaft that is a safety screw in case the nut gets loose. Then undo the nut. You can now undo the large plastic nut that is used to adjust the length of the cord, remembering that this is a right hand threaded nut. Care should be taken to count the pieces and remember their order. Not critical but it helps to put things back. If you have dropped them you should be able to put them back in the proper order as they fit into slots in each other so the order should become clear. As you take the big nut off which does the adjustment of the length of cord do catch the spring! You now have the spooler onto which you can wind your cord. You will probably have to undo some of the old stuff first. I have tried a number of methods of securing the new bit and the one I'm currently using is to cut a length, then double it up. Then put the two free ends through the loop and place over the spooler and put tight. Then wind it around. I think I went in the direction of the arrow. Sorry cannot remember that bit. Don't think it matters. You will now have to feed the two free ends into the holes through which they then extend to do the cutting. A bit fiddly as the other end tries to unwind. Don't forget to check that you are putting the spooler the right way around. It has two protruding posts which slot into the other half. Replace the spacer on the spindle of the strimmer, now the spooler, then the washer and securing nut and finally the screw to secure it all.
John Liechti, June 2008