private const string taskName = "UpdateTileBackgroundTask"; // class name
private const string taskEntryPoint = "fullNamespacenamespaceOfBackgroundTaskProject.UpdateTileBackgroundTask";

// on launched add  RegisterBackgroundTask();
// add appmanifest to run in background
private async void RegisterBackgroundTask()
{
	        var status = BackgroundExecutionManager.GetAccessStatus();

                if (status == BackgroundAccessStatus.Unspecified || status == BackgroundAccessStatus.Denied)
                {
                    var backgroundAccessStatus = await BackgroundExecutionManager.RequestAccessAsync();

                    if (backgroundAccessStatus == BackgroundAccessStatus.AllowedMayUseActiveRealTimeConnectivity ||
                        backgroundAccessStatus == BackgroundAccessStatus.AllowedWithAlwaysOnRealTimeConnectivity)
                    {
                        foreach (var task in BackgroundTaskRegistration.AllTasks)
                        {
                            if (task.Value.Name == taskName)
                            {
                                task.Value.Unregister(true);
                            }
                        }

                        BackgroundTaskBuilder taskBuilder = new BackgroundTaskBuilder();
                        taskBuilder.Name = taskName;
                        taskBuilder.TaskEntryPoint = taskEntryPoint;
                        taskBuilder.SetTrigger(new TimeTrigger(15, false));
                        var registration = taskBuilder.Register();
                    }
                }
}