When you have a reward, go visit the Goddess. You should be able to do a reward with her. She has two options. Serviced and JOY. The game will randomly pick from one of those. .You may have to try a few times giving her a reward to get the right scene. You can always say NO when she tells you what your reward is at the beginning of the scene, which should prevent you from losing your reward stone.
Hope that helps!