Confusion connecting iOS portion of Flutter App to Firebase

In the given (predefined) AppDelegate class, there are 2 things you need to do additionally. They are

import Firebase  // <-- 1st add

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
    override func application(_ application: UIApplication,didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?
    ) -> Bool {
        GeneratedPluginRegistrant.register(with: self)

        FirebaseApp.configure() // <-- 2nd add

        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }
}

Merge both code together:

import UIKit
import Flutter
import Firebase

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?
    ) -> Bool {
        GeneratedPluginRegistrant.register(with: self)
        FirebaseApp.configure()
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }
}