Change/update Firebase notification token or instance id forcefully via code?

Now i got my answer after facing many troubles for generating new or change token of firebase for push notification.

1) Delete old Firebase token

let instance = FIRInstanceID.instanceID()
_ = FIRInstanceID.delete(instance)
FIRInstanceID.instanceID().delete { (err:Error?) in
    if err != nil{
        print(err.debugDescription);
    } else {
        print("Token Deleted");
    }
}

2) Request new Firebase token

if let token = FIRInstanceID.instanceID().token() {
    print("Token \(token) fetched");
} else {
    print("Unable to fetch token");
}

FIRMessaging.messaging().connect { (error) in
    if (error != nil) {
        print("Error connecting to FCM. \(error.debugDescription)")
    } else {
        print("Connected to FCM.")
    }
}

UPDATE FOR SWIFT 4 & Firebase 4.8.2 (Follow simple two steps)👇👇

1) Delete old Token

let instance = InstanceID.instanceID()
instance.deleteID { (error) in
    print(error.debugDescription)
}

2) Request for new token

if let token = InstanceID.instanceID().token() {
    print("Token : \(token)");
} else {
    print(“Error: unable to fetch token");
}

Messaging.messaging().shouldEstablishDirectChannel = true

You can get updated token in MessagingDelegate method didReceiveRegistrationToken and in Refresh Token.

func messaging(_ messaging: Messaging, didReceiveRegistrationToken fcmToken: String) {
    print("Firebase Token :  \(fcmToken)")
}

UPDATED FOR FIREBASE MESSAGING 7.3.0

class func regenerateFCM(){
    Installations.installations().delete { (err) in
        if let err = err {
            print(err)
        }else{
            Installations.installations().authTokenForcingRefresh(true) { (result,err) in
                if let result = result {
                    print(result)
                   
                    Messaging.messaging().deleteToken { (err) in
                        if let err = err {
                            print(err)
                        }else{
                            print("FCM TOKEN DELETED")
                            Messaging.messaging().token { (token, err) in
                                if let token = token {
                                    print("NEW FCM TOKEN GENERATED")
                                    print(token)
                                }
                                if let err = err {
                                    print("ERROR WHILE GENERATING NEW FCM TOKEN")
                                    print(err)
                                }
                            }
                        }
                    }
                    
                }else if let err = err {
                    print(err)
                }
            }
        }
    }
}

UPDATE FOR FIREBASE 8.5.0

Messaging.messaging().deleteToken { err in
        if let err = err {
            print("Error while generating new FCM Token")
            print(err)
        }else{
            Messaging.messaging().token { token, err in
                 if let token = token {
                    print("NEW FCM TOKEN GENERATED")
                    print(token)
                }
            }
        }
    }

for now InstanceID.instanceID().token() is deprecated.

You should use this:

let instance = InstanceID.instanceID()
instance.deleteID { (error) in
  print(error.debugDescription)
}

instance.instanceID { (result, error) in
  if let error = error {
    print("Error fetching remote instange ID: \(error)")
  } else {
    print("Remote instance ID token: \(String(describing: result?.token))")
  }
}
Messaging.messaging().shouldEstablishDirectChannel = true

Then in AppDelegate:

extension AppDelegate: MessagingDelegate {

func messaging(_ messaging: Messaging, didReceiveRegistrationToken fcmToken: String) {
    //Here is your new FCM token
    print("Registered with FCM with token:", fcmToken)
}