Stir together peaches, lemon juice, sugar, vanilla, and salt a in medium bowl. Let stand 15 minutes, stirring occasionally. Drain peaches, reserving 1 tablespoon liquid. Whisk cornstarch into reserved liquid; stir into drained peaches. Cut piecrusts into 8 (4-inch) circles. Place about 1 tablespoon filling in center of each circle. Brush edges of dough with water; fold dough over filling to form half-moons. Crimp edges with a fork to seal; cut 3 small slits in top of pies. Coat pies well with cooking spray. Place 3 pies in single layer in air fryer basket, and cook at 350°F until golden brown, 12 to 14 minutes. Repeat with remaining pies.