If you store your apple crisp correctly, you can prevent it from turning soggy. To store your apple crisp properly, you can cover it in paper towels or plastic wrap. Make sure to cover the whole of the top of the apple crisp with paper towels and plastic wrap to protect your apple crisp. Once you have correctly covered your apple crisp, leave your apple crisp at room temperature. This will stop your apple crisp from coming into contact with moisture. If this still does not work and your apple crisp  has turned soggy, you can reheat it in the oven to crisp up the top layer. To do this preheat your oven to 300 degree Fahrenheit and place your apple crisp in an oven safe dish. Heat your apple crisp for 10 minutes or until the top of the apple crisp  starts to turn a golden brown. This will help your soggy apple crisp to turn crunchy again.