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First create the UINavigationController, giving it a rootViewController as your controller to display.

Then create a UIBarButtonItem with a button and action select target as a method in your class.

Then add that to your UINavigationController's topViewController's navigationItem.

let navigationController = UINavigationController(rootViewController: YOUR_CONTROLLER)
let btnDone = UIBarButtonItem(title: "Done", style: .done, target: self, action: #selector(dismissNav))
navigationController.topViewController?.navigationItem.rightBarButtonItem = btnDone

The referenced selector would look like this:

func dismissNav() {
    self.dismiss(animated: true, completion: nil)
}