Remove the blinds from the window by pulling the headrail free from the housing. Lay the blinds on a flat surface. Use a Philips-head screwdriver to remove the caps on either end of the headrail, if your wooden blinds have them.
Untie the knot in the lift cords. Pull the cords up through the holes in the headrail.
Thread the cords under the first pin on the left side of the cord lock, and over the round pin in the middle. Thread the cords under the third pin, then push them through the holes in the headrail.
Push the cord lock assembly into the housing on the headrail so it is just above the holes in the headrail. The back of the cord lock assembly will snap into place in the lip of the headrail.
Retie the knots in the cords. Push the end caps back over the ends of the headrail. Replace the wooden blinds in the housing over the window.