Combine diced apples, brown sugar, butter, and cinnamon in a nonstick skillet. Cook over medium heat until apples soften, about 5 minutes.

Dissolve cornstarch in cold water. Stir into apple mixture and cook until sauce thickens, about 1 minute. Remove from heat and let cool.

Unroll pastry crust on a lightly floured surface. Cut into 8 rectangles, slightly smoothing the surface, and prepare to fill pies.

Place filling on the center of 4 dough rectangles, wet outer edges with water, and cover with remaining 4 rectangles. Crimp edges with a fork and cut 4 small slits in the tops.

Preheat air fryer to 385°F (195°C). Spray the basket with cooking spray and brush the tops of 2 pies with grapeseed oil.

Insert pies into air fryer and bake until golden brown, about 8 minutes. Repeat for the remaining pies.