Top or side?
The side where the tunnel with the cords are located are the sides of the mouth cap. Often the top and bottom are mistaken as sides and they don't fit well on your head. So turn a quarter turn...
If you put on 2 cords per tunnel, a model will appear in the mouth cap.
Customize it yourself
You can tailor the cords yourself by tying a tight overhand knot at the desired length. You can cut the ends of the cords. Then you pull the button into the tunnel of the mouth cap.
After wearing them - preferably every day - put them in a bowl of boiling water for a while to kill the bacteria: Place the mouth cap(s) in the bowl and pour boiling water on it. Possibly with a drop of hand soap for freshness. When the water has cooled, rinse and hang to dry. In addition to the bowl with boiling water, you can also occasionally wash the mouth cap in the washing machine at 30 or max 40 degrees (in a washing bag).