Turn off the string trimmer and then lay the trimmer down with the head facing up.
Remove the spool retainer on the bottom of the head by pushing in the tabs and then pulling the retainer off.
Lift the spool off the head and remove any remaining string.
Insert one end of the string into the string anchor hole on the upper portion of the spool and then wind the string around the spool in the direction of the arrows on the spool, often clockwise.
Place the string through the string slot on the spool, allowing approximately 6 inches of string to remain outside the spool.
Place the spool back onto the trimmer head and then press the spool retainer back into position to secure the spool.