code: public void unregisterPushServices(TaskCompletionListener completionListener) {
          RespokeClient activeInstance = null;
  
          // If there are already client instances running, check if any of them have already connected
          for (RespokeClient eachInstance : instances) {
              if (eachInstance.isConnected()) {
                  // The push service only supports one endpoint per device, so the token only needs to be registered for the first active client (if there is more than one)
                  activeInstance = eachInstance;
                  break;
              }
          }
  
          if (null != activeInstance) {
              activeInstance.unregisterFromPushServices(completionListener);
          } else {
              postTaskError(completionListener, "There is no active client to unregister");
          }
      }
docs: Unregister this device from the Respoke push notification service and stop any future notifications until it is re-registered
  
  @param completionListener  A listener to be notified of the success of the asynchronous unregistration operation