input: def delete_item_from_list(item_name: str) -> str:
      """ Deletes an item from a given list if it exists.
      If the item is successfully deleted, it returns a success message.
      If the item does not exist, it returns a message indicating the item was not found.
      >>> delete_item_from_list("Apple")
      "Item successfully deleted."
      >>> delete_item_from_list("Mango")
      "Item not found."
      """
      items = ["Apple", "Banana", "Orange"]
      if item_name in items:
          items.remove(item_name)
          return "Item successfully deleted."
      else:
          return "Item not found."
output:     items = ["Apple", "Banana", "Orange"]
      if item_name in items:
          items.remove(item_name)
          return "Item successfully deleted."
      else:
          return "Item not found."