Ionic3 Push notification with firebase

Question

Hello, I’m trying to use the Ionic push plug-in , with firebase but he’s asking me to do one thing. but I can’t find it and solve it

import UIKit
import Firebase

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

  var window: UIWindow?

  func application(_ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?)
    -> Bool {
    FirebaseApp.configure()
    return true
  }

I have Xcode on my mac