Measure the width of the upper track above the window and write down the measurement. Place the tape measure at the top of the curtain track and measure all the way down to the floor. Write down this measurement as well. Use a step stool if you cannot reach the track easily from the floor.
Add the two measurements together and add an additional 6 inches. Multiply the number by 2, since the cord is a loop, to arrive at the total length needed for the cord.
Examine each end of the track where it attaches to the wall and remove the screws that hold it in place. Set the screws in a safe area and pull the track down from the wall. Set it on a table with the open side facing upward so you can see the pulleys.
Look at the left side of the track to locate the pulley, which is small wheel. Push the end of the cord up along the outer edge of the pulley and then move it over the top until it extends into the horizontal track.
Grasp the free end of the cord inside the horizontal track using a pair of needle-nose pliers. Pull it through the track and under the sliders that hold the curtains.
Push the end of the cord under the left carrier. Open a paper clip and insert the end into the left hole of the carrier to pull the cord up through it. Tie the end in a double knot so that it does not fall back through the hole.
Locate the other end of the cord and thread it up into the pulley and through the track just as you did the first end. When you reach the carrier, thread it underneath it and continue down until you reach the second carrier. Insert the end under the carrier and bring it up through the first hole using the paper clip.
Turn the end downward and push it through the second hole in the carrier and back into the track. Pull the cord through the track until it is tight. Slide it under the plastic curtain sliders until you reach the right end of the track.
Slide the cord through the middle of the two pulleys on the right side and then down out of the track. Pull out as much cord as possible and then push the free end back up and over the top pulley until it re-enters the horizontal track.
Slide the end underneath the curtain sliders and the right carrier until you arrive at the left carrier. Slide the cord end up through the hole in the carrier and tie the end in a double knot.
Mount the track back up over the window by reinserting the screws. Hang the curtain panels.