Practice from ready position. Knee lifts center line but not as high as front kick. Point foot and toes. Bring foot up beneath groin, hitting with instep (if you’re too close, you can use shin). Snapping kick. Think of driving the testicles upward into the groin from below. Pull back. Set down. Alternate sides.
Try to remain upright. Speed matters more than power. Hip extension not required to be effective.