How do i replace pull string on craftsman 20/14 chainsaw

Remove the cover containing the cord rewind mechanism, untie the cord's knot in the center of the mechanism and remove the old cord by unwinding it from the pulley. Thread the new cord through the hole it goes through on the outside and wind the recoil mechanism so that it has sufficient spring tension to rewind the new cord. Use something appropriate to immobilize the pulley while you thread the cord through the center and tie the knot. Slowly allow the pulley to retract and wind the new cord onto it. Replace the cover. As an aside, sometimes when the cord breaks and the pulley snaps back quickly, the rewind spring can break.