func changeRootViewController(with viewController: UIViewController) {
guard let oldViewController = self.window?.rootViewController else { return }
UIView.transition(from: oldViewController.view, to: viewController.view, duration: 0.3, options: [.transitionCrossDissolve, .allowAnimatedContent]) { _ in
    self.window!.rootViewController = viewController
    self.window!.makeKeyAndVisible()
    oldViewController.dismiss(animated: false) {
        oldViewController.view.removeFromSuperview()
    }
}
}

let appDelegate = UIApplication.shared.delegate as? AppDelegate
appDelegate?.changeRootViewController(with: MyNewViewController())