Place the majority of your weight on the seat of the chair
The name kneeling chair can be misleading as it may lead you to believe that your knees are replacing the function of your bottom and taking the bulk of your weight. Like with any other chair, your bottom should still be carrying the bulk of your weight. The cushions beneath the seat are simply there to act as a support for your shins, helping you keep your balance and stop you from sliding off the tilted seat.
Begin by sitting bottom first on the seat before moving your legs and shins into a kneeling position. If you get the sensation that you are being pushed forward and onto the shin cushions, try sitting even further back on the seat of the chair. Another thing to be aware of is the distance between your chair and the table in front of you. If you are leaning at an exaggerated angle, this might put unnecessary pressure on your shins. Bringing your kneeling chair closer to your desk or tabletop will help you avoid this.