Remove bolts from the starter cord housing using a wrench. Remove the housing from the Toro lawn mower. Flip the housing over and check the spring to be sure it is still good.
The spring is still good if you turn the pulley and it springs back on its own. Cut the old cord from the starter pulley. Twist the pulley several times to add tension to the spring.
Insert a screwdriver into a hole in the pulley to hold it still when you insert the new starter cord. Insert the new starter cord through the opening of the housing and into the hole on the pulley. Tie a knot at the end of the string.
Allow the pulley to slowly spin around to its original position. As it turns, it will draw the string into the housing. Place the housing on top of the lawn mower. Install the bolts and tighten them snugly using a wrench. Pull the cord several times to test it, making sure it goes back into the housing properly.