Locate the "Tap" button located on the bottom of the trimmer head and pull out on it to remove the tap button and spool from the trimmer head.
Remove what is left of the old string from the trimmer head by unwinding it and then discard the old string.
Cut a 25 ½-inch piece of trimmer string and then cut a second piece the exact same length.
Place ½ inch of the tip of one string into the hole in the side of the spool located the furthest away from the trimmer's tap button and then wind the string in the direction indicated by the arrow on the spool. Leave approximately 5 inches of string off the spool and then lock the string into the notch on the spool's outside edge.
Repeat step 4 but use the hole in the spool closest to the tap button.
Place the spool into the trimmer head and align the notches with the eyelets in the trimmer head. Feed the strings through the notches and then snap the trimmer head into place.
Pull hard on each string to pull the string out of the notches on the spool.