public void Rotate( 
   SelectionSet features,
   MapPoint origin,
   double angle
)

// Rotates the selected features by a specified angle.
await QueuedTask.Run(() =>
  {
    var rotateFeatures = new EditOperation() { Name = "Rotate Features" };

    //Rotate works on a selected set of features
    //Get all features that intersect a polygon
    //Rotate selected features 90 deg about "origin"
    rotateFeatures.Rotate(MapView.Active.GetFeatures(polygon), origin, angle);

    //Execute to execute the operation
    //Must be called within QueuedTask.Run
    if (!rotateFeatures.IsEmpty)
    {
      //Execute and ExecuteAsync will return true if the operation was successful and false if not
      var result = rotateFeatures.Execute();
      //or use async flavor
      //await rotateFeatures.ExecuteAsync();
    }
  });