To use the Kick Dummies, first tap the Kick Dummy icon in the Ninja Kit. Select one of the Kick Dummies and place it in the environment.  

One the Kick Dummy has been placed, the Ninja will start sparring. Keep the Kick Dummy inside the sparring area, which is marked with a circle on the ground, to complete the training. If the circle turns red, you'll need to use your finger to drag the Kick Dummy back into the sparring area.