Spiritual teacher Mingour Rinpoche says unhappy born persons can change to happy persons – but how can they change this?

at 4:52 in this video: spiritual teacher Mingour Rinpoche who was gunea pig in the the following scientific study of Richard Davidson: https://www.pnas.org/doi/10.1073/pnas.0407401101 says if we are born unhappy, we will not always be unhappy, we can change. And he reports about the scientific studies in which he participated. But are there any living examples …