Remove the outer cap off the top tension unit by unscrewing the center screw.
Adjust the inner nut until the best tension is achieved.
The parts inside the outer dial are shown in order. Replace them as shown then replace the outer dial onto the tension stud with the red line at 4.5. This will give you the best range of adjustment once the dial is back together. The tension you are trying to get is for the knot to form in the center of the fabric.