input: def delete_item_from_list(items: List[str], item_to_delete: str) -> str:
      """ Deletes an item from the list if it exists and returns a message indicating the result.
      If the item exists in the list, it will be removed and a success message will be returned.
      If the item does not exist in the list, a message indicating that it was not found will be returned.
      
      >>> delete_item_from_list(["Apple", "Banana", "Orange"], "Banana")
      'Item successfully deleted.'
      
      >>> delete_item_from_list(["Apple", "Banana", "Orange"], "Pineapple")
      'Item not found.'
      """
output:     if item_to_delete in items:
          items.remove(item_to_delete)
          return 'Item successfully deleted.'
      else:
          return 'Item not found.'