Remove the blinds from the window. Pull the old cord down and out of the blinds. Remove the side caps and slide the top and bottom plastic covers off the blinds.
Select the small cord guides for the 3/8-inch pleated blinds and the larger guide for the 3/4-inch pleated blinds. Push the cord guide into the hole in the top cell and filler strip on the top of the blinds. Only put the guide in the head rail cell.
Measure out the cord length. Add the shade height to the shade width and add 24 to get the total length for one cord, for the stop ball shades. For block and tackle shades, multiply the shade length by two, add shade width and 24 for the total cord length. Each hole needs its own length of cord.
Push the threading tool up through the bottom of the blinds and into the cord guide. Thread the cord through the guide. Push the guide and cord down into the blinds, through each hole. For block and tackle blinds, push the thread from the top to the bottom, and thread it back up through the blinds in the holes parallel to the first set of holes.
Tie a knot at the end of the cord to secure it. Replace the plastic covers onto the blinds and replace the side caps.