follow below step to add FCM in your swift Project

1- If you don't have an Xcode project yet, create one now. Create a Podfile if you don't have one:

$ cd your-project directory
$ pod init

2- Add the pods that you want to install. You can include a Pod in your Podfile like this:

pod 'Firebase/Core'
pod 'Firebase/Messaging'

3- Install the pods and open the .xcworkspace file to see the project in Xcode.

$ pod install
$ open your-project.xcworkspace

4- Download a GoogleService-Info.plist file from plist and include it in your app.

5- Upload APNs certificate to Firebase. APN Cert

6- add "import Firebase" in your appDelegate file of project

7- add this "FIRApp.configure()" in your "application:didFinishLaunchingWithOptions"

8- register for remote notification

  if #available(iOS 10.0, *) {
  let authOptions : UNAuthorizationOptions = [.Alert, .Badge, .Sound]
  UNUserNotificationCenter.currentNotificationCenter().requestAuthorizationWithOptions(
    authOptions,
    completionHandler: {_,_ in })

  // For iOS 10 display notification (sent via APNS)
  UNUserNotificationCenter.currentNotificationCenter().delegate = self
  // For iOS 10 data message (sent via FCM)
  FIRMessaging.messaging().remoteMessageDelegate = self

} else {
  let settings: UIUserNotificationSettings =
  UIUserNotificationSettings(forTypes: [.Alert, .Badge, .Sound], categories: nil)
  application.registerUserNotificationSettings(settings)
}

application.registerForRemoteNotifications()

9- to get register token use

let token = FIRInstanceID.instanceID().token()!

10- and if u want monitor for token change use below code in appDelegate file

func tokenRefreshNotification(notification: NSNotification) {
if let refreshedToken = FIRInstanceID.instanceID().token() {
    print("InstanceID token: \(refreshedToken)")
  }

  // Connect to FCM since connection may have failed when attempted before having a token.
  connectToFcm()
}

11- to recieve message from fcm add below code in appDelegate

func connectToFcm() {
  FIRMessaging.messaging().connectWithCompletion { (error) in
    if (error != nil) {
      print("Unable to connect with FCM. \(error)")
    } else {
      print("Connected to FCM.")
    }
  }
}

12- and for disconnect use

func applicationDidEnterBackground(application: UIApplication) {
  FIRMessaging.messaging().disconnect()
  print("Disconnected from FCM.")
}

in your appDelegate.

the initialization complete and client ready to recieve message from fcm panel or send by token from third party server