public ParcelEditToken AssignFeaturesToRecord( 
   ParcelLayer parcelLayer,
   SelectionSet sourceFeatures,
   ParcelRecord parcelRecord
)

 string errorMessage = await QueuedTask.Run(() =>
{
   //check for selected layer
   if (MapView.Active.GetSelectedLayers().Count == 0)
    return "Please select a source feature layer in the table of contents.";
   //first get the feature layer that's selected in the table of contents
   var srcFeatLyr = MapView.Active.GetSelectedLayers().OfType<FeatureLayer>().FirstOrDefault();
  var myParcelFabricLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<ParcelLayer>().FirstOrDefault();
  if (myParcelFabricLayer == null)
    return "No parcel layer found in the map.";
  try
  {
    var theActiveRecord = myParcelFabricLayer.GetActiveRecord();
    if (theActiveRecord == null)
      return "There is no Active Record. Please set the active record and try again.";
    var editOper = new EditOperation()
    {
      Name = "Assign Features to Record",
      ProgressMessage = "Assign Features to Record...",
      ShowModalMessageAfterFailure = true,
      SelectNewFeatures = true,
      SelectModifiedFeatures = false
    };
     //add parcel type layers and their feature ids to a new Dictionary
     var ids = new List<long>(srcFeatLyr.GetSelection().GetObjectIDs());
    var sourceFeatures = new Dictionary<MapMember, List<long>>();
    sourceFeatures.Add(srcFeatLyr, ids);
    editOper.AssignFeaturesToRecord(myParcelFabricLayer,
      SelectionSet.FromDictionary(sourceFeatures), theActiveRecord);
    if (!editOper.Execute())
      return editOper.ErrorMessage;
  }
  catch (Exception ex)
  {
    return ex.Message;
  }
  return "";
});
 if (!string.IsNullOrEmpty(errorMessage))
   MessageBox.Show(errorMessage, "Assign Features To Record.");