Process Silent Push Notification when iOS app is in background

I have implemented push notification and subscribe app on different news topics. When a silent push notification received i want my app to subscribe/unsubscribe the topic on type based. But problem i am facing is when app is in background code executed and hit the subscribe/unsubscribe code but app wont process it and as soon as i open the app i got message that topic has been subscribed/unsubscribe successfully. While in foreground code is executing and processing successfully. Background processing and Background fetch are enabled in background modes. My Code is as:

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any], fetchCompletionHandler
                   completionHandler: @escaping (UIBackgroundFetchResult)
                     -> Void) {
    if let messageID = userInfo[gcmMessageIDKey] {
      print("/// Message ID: \(messageID)")
    }
      if let topic = userInfo["topic"] as? String{
          if let type = userInfo["type"] as? String{
              do {
                  if(type == "unsubscribe"){ 
             Messaging.messaging().unsubscribe(fromTopic: topic)                
                  } else {
            Messaging.messaging().subscribe(toTopic: topic)
                  }
                }catch{
              }
          }
      }

    // Print full message.
    print("info = ", userInfo)
    Messaging.messaging().appDidReceiveMessage(userInfo)
    completionHandler(UIBackgroundFetchResult.newData)
}

My Headers from postman are

apns-push-type:background
apns-priority:10

and the body

{
  "to" : "*** device token ***",
  "priority" : "high",
  "content_available": true,
  "data" : {
    "topic" : "Sports",
    "type" : "unsubscribe" // subscribe
  } 
}

What i want is to subscribe/unsubscribe the fcm topics when app is in background and silent notification received.