Ios 以编程方式更改VC&39；S导航栏按钮的属性，以响应另一个VC中的按钮按下

我已经在MainViewController中创建了一个导航栏按钮

override func viewDidLoad() {
    super.viewDidLoad()    

    navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Save", style: .plain, target: self, action: #selector(presentPopup))
        
}
    
@objc func presentPopup() {
        
    let popupVC = PopupViewController()
    popupVC.modalPresentationStyle = .overCurrentContext
    present(popupVC, animated: true, completion: nil)
        
}

它显示用于保存主视图内容的弹出表单(包含"保存"按钮).我想让这个"保存"按钮(在PopupViewController):(1)将S导航栏按钮的标题改为"已保存"；(2)禁用该按钮.

到目前为止，我在PopupViewController人中有以下几点:

let popupBox: UIView = {
    let view = UIView()
    view.translatesAutoresizingMaskIntoConstraints = false
    return view
}()

let button: UIButton = {
    let view = UIButton()
    view.translatesAutoresizingMaskIntoConstraints = false
    return view
}()

override func viewDidLoad() {
    super.viewDidLoad()
        
    self.definesPresentationContext = true
    view.backgroundColor = .clear
        
    view.addSubview(popupBox)
    // configure popupBox

    view.addSubview(button)
    // configure button
    button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
        
}

@objc func buttonAction(_ sender: UIButton) {
    // save main VC's contents
    // change title of main VC's nav button - WHAT GOES HERE?
    // disable main VC's nav button - WHAT GOES HERE?
    self.dismiss(animated: true)  // dismiss popup
    
}

我应该在按钮的操作中添加什么来完成我想做的事情？