Hi Jaaki,
I think the cord size is 1.5mm and there should be a quick release cover system via two buttons on either side of the cord reel. The reel should then pop put. There will be two holes to feed the cord into and directional arrows telling you which way to wind the cord. Just keep winding the cord trying to keep the cord tightly wound, a bit like cotton or thread on a reel, and keep going until the cord nearly reaches the outside of the reel. Cut the cord, and then keep your finger on the wound cord. You will then see the “gear” mechanism for fixing the cord reel back into the strimmer. Click into place and replace the cover.
Mikey, July 2005