public class MapSurround : Element, ArcGIS.Desktop.Mapping.IElement, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IDisposable, System.IEquatable<Element>  

//Added references
using ArcGIS.Desktop.Core;                         //Project
using ArcGIS.Desktop.Layouts;                      //Layout class
using ArcGIS.Desktop.Framework.Threading.Tasks;    //QueuedTask

public class MapSurroundExample
{
  public static Task<bool> UpdateMapSurroundAsync(string LayoutName, string SBName, string MFName)
  {
    //Reference a layoutitem in a project by name
    LayoutProjectItem layoutItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals(LayoutName));
    if (layoutItem == null)
      return Task.FromResult(false);

    return QueuedTask.Run<bool>(() =>
    {
            //Reference and load the layout associated with the layout item
            Layout lyt = layoutItem.GetLayout();

            //Reference a scale bar element by name
            MapSurround scaleBar = lyt.FindElement(SBName) as MapSurround;
      if (scaleBar == null)
        return false;

            //Reference a map frame element by name
            MapFrame mf = lyt.FindElement(MFName) as MapFrame;
      if (mf == null)
        return false;

            //Set the scale bar to the newly referenced map frame
            scaleBar.SetMapFrame(mf);
      return true;
    });
  }
}

//Update a map surround.

//Perform on the worker thread
QueuedTask.Run(() =>
{
  // Reference and load the layout associated with the layout item
  Layout layout = layoutItem.GetLayout();
  if (layout != null)
  {
    // Reference a scale bar element by name
    MapSurround scaleBar = layout.FindElement("MyScaleBar") as MapSurround;

    // Reference a map frame element by name
    MapFrame mf = layout.FindElement("MyMapFrame") as MapFrame;

    if ((scaleBar != null) && (mf != null))
      //Set the scale bar to the newly referenced map frame
      scaleBar.SetMapFrame(mf);
  }
});