swift set initial view controller
// For Swift 4.2 and 5 code:
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool { 
     self.window = UIWindow(frame: UIScreen.main.bounds)
     let storyboard = UIStoryboard(name: "Main", bundle: nil)
     let initialViewController = storyboard.instantiateViewController(withIdentifier: "dashboardVC")
     self.window?.rootViewController = initialViewController
     self.window?.makeKeyAndVisible()
}
// For Xcode 11+ and for Swift 5+ :
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
     var window: UIWindow?
     func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
         if let windowScene = scene as? UIWindowScene {
             let window = UIWindow(windowScene: windowScene)
              window.rootViewController = // Your RootViewController in here
              self.window = window
              window.makeKeyAndVisible()
         }
    }
}
