In a 3-qt. slow cooker, combine chicken, dressing mix and wing sauce.

Cook, covered, on low until chicken is tender, 3-4 hours.

Preheat oven to 425°. Shred chicken with 2 forks; stir in butter.

With a corner of an egg roll wrapper facing you, place 3 tablespoons chicken mixture just below center of wrapper; top with 1 teaspoon each feta and mozzarella cheeses. (Cover remaining wrappers with a damp paper towel until ready to use.) Fold bottom corner over filling; moisten remaining wrapper edges with water. Fold side corners toward center over filling; roll up tightly, pressing at the tip to seal.

Place on a parchment-lined baking sheet, seam side down. Repeat, adding additional baking sheets as needed.

Bake until golden brown, 15-20 minutes. Let stand 5 minutes before serving.

Serve warm, with ranch dressing for dipping if desired.