Saving a workout as a favorite requires a LogCard, because the favorites are actually saved on the LogCard. When using a LogCard, the monitor will prompt you to save a workout as a favorite anytime you set up a new workout (predefined or custom workouts cannot be saved as favorites.) Select Yes when prompted, and then select which Favorite you want to replace. (Until you begin saving your own favorites, the Favorites list on the monitor will match the Custom list.)
Each LogCard holds five favorites. You can also copy favorites to the Custom List, and then set up five new favorites for a total of 10 personalized workouts.