Place the frozen blueberries in a microwave-safe bowl and heat on the defrost mode (about power 3) until the blueberries are soft and have released some juice, about 3 minutes. In a small glass or bowl, scoop some of the blueberries and juices into the bottom. Layer with the Greek yogurt, granola, agave nectar, and more blueberries. Serve. Stir together before eating, if you wish.