This site names this specific bonus guide directly as Bonus 3: the Connection Guide.
This site describes it directly as practical tips for building a stronger connection — worth reading it alongside the similarly themed Intimacy Guide and Preliminaries Guide, since all three touch on relationship-building specifically.
Worth noting three of the five bonus guides — Intimacy, Connection and Preliminaries — share a relationship-focused theme, while the other two address habit-formation and personalized usage specifically.