Open the umbrella and locate the area where the umbrella cord has broken or worn through. Around the winding bolt is the normal wear location for most sun umbrellas, because of the amount of stress on the cord.
Remove the retaining rings from the winding bolt or crank. To do this, push the putty knife blade between the retaining ring and the crank. Push on the ring to loosen it. Use a screwdriver to apply force, and push the ring off the winding device. Unscrew the crank housing and remove outer part of it from the device.
Pull the cord completely out of the umbrella. Some will have the cord inside the pole, while others will have the cord running outside the pole
Insert the end of the new cord into the end of the pick-up tool. Use the pick-up tool to thread the cord through the pole, or through the rings outside the pole. These tools can be found at most patio and lawn-care stores.
Tie the end of the cord to the ring at the top of the umbrella. The knot must be secure.
Place the pick-up tool into the hole on the crank and thread the cord through the hole. Thread eight to 10 inches of cord through the hole, and tie it to the crank. Shove that knot into the hole on the crank. This will hold the cord in place.
Place the outer housing and rings back onto the crank, and tighten them with a screwdriver. Push the retaining rings back onto the crank, and gently tap them into place with the screwdriver.