The adjustable knot is simply a static knot through which the bracelet cords move. It pinches the bracelet cords together and keeps them firmly in place.
To open the adjustable knot simply pull apart on the two 8mm end beads (silver in this photo). The bracelets cords will travel through the static knot and the circumference of the bracelet will increase. ALWAYS pull on the beads closest to the knot to open the bracelet.
To close the knot after putting the bracelet on your wrist simply pull apart on the two beads on the ends of the dangling bracelet cords. The cords will travel through the static knot and the bracelet will close on your wrist.