The dump cake is finished baking when the cake topping is puffed and browned on the top and the fruit is bubbling and juicy. Let the cake cool completely to help the filling set, which makes the cake easy to serve.
Preheat oven to 350°. Toss blueberries with cinnamon; spread into a greased 13x9-in. baking dish. Drizzle with half the melted butter. Sprinkle with cake mix; drizzle with remaining butter.
Bake until golden brown and fruit is bubbly, 45-55 minutes. Cool on a wire rack.
Beat together yogurt, whipped topping, marshmallow creme and lemon curd. Serve dump cake with yogurt mixture and, if desired, additional blueberries.