In a large bowl, whisk together the Bisquick, sugar, and cinnamon.
Add the milk and stir until a soft dough forms.
Stir in the diced apples.
Use an ice cream scoop to form the fritters, placing each scoop in the greased air fryer basket.
Brush the fritters with melted butter, then cook in the preheated air fryer for 8 to 10 minutes, until the fritters are golden brown and cooked through.
Continue cooking in batches until all the batter has been used.
Transfer the cooked fritters to a wire cooling rack.
Make the glaze by whisking together the powdered sugar, vanilla, and three tablespoons of milk. If the glaze is too thick, add more milk until the desired consistency has been reached.
Drizzle the glaze over the cooled fritters and allow it to harden before serving.