Sometimes a pull cord for a blind gets stuck, needing repair--or breaks, requiring replacement. You can purchase replacement cords for your blinds from companies over the Internet or at your local hardware or building-supply store. Different-size blinds require specific cord widths; and since different styles of blinds might have their own stringing methods, it is best to refer to the manufacturer's installation guide for specific information on replacement-cord widths and restringing instructions when planning this project.
Remove the cap covering the hole in the bottom rail of the venetian blinds. You can do this with your hands and fingers. Look for the end of the cord, where it is tied in a knot. Pull the cord toward you, and cut the knot off the end of the cord.
Hold the end of the new cord in your hand. Light a lighter, and catch the end of the new cord on fire. Immediately blow out the flame. Attach the old cord and new cord together. This will melt the ends of the cords together.
Carefully, roll the hot, melted ends together between your fingertips to bond the cords together. Press gently so you don't burn yourself. When the ends are bonded after a minute or so, gently tug on the cord connection to ensure that the ends are bonded securely. If not, repeat the lighting procedure.
Pull on the tassel or lift cord, and it should string right through the blind. Tie a new knot in the cord at the bottom rail, and replace the rail cap.
Take the blinds down according to the manufacturer's instructions. You might just need to take the cover off the header with a flathead screwdriver and pull the blinds out of a slot.
Take out the old cord, and remove any tassels or pulls. You might need to cut it with scissors to make this easier. Insert the new cord through the cord lock and head rail.
Feed the new cord through each of the blind slats. Feed it through the bottom rail, and tie a knot that is big enough that it won't come through the hole.
Replace any tassels or pulls, and tie a knot to secure. Re-hang the blinds.