iOS window rootviewcontroller 변경

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        print("ViewController 스토리보드: \(self.storyboard)")
    }


    @IBAction func changeRootVC(_ sender: UIButton) {
        let sb = UIStoryboard(name: "SB2", bundle: nil)
        let vc2 = sb.instantiateViewController(withIdentifier: "VC2") as! VC2
        let ad = UIApplication.shared.delegate as! AppDelegate
        ad.window?.rootViewController = vc2
    }
    
}

first vc에서 Button 클릭