public void SetCamera( 
   Envelope extent
)

//Set the extent of a map frame to the envelope of a feature.

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  //Reference MapFrame
  MapFrame mf_env = layout.FindElement("Map Frame") as MapFrame;

  //Get map and a layer of interest
  Map m = mf_env.Map;
  //Get the specific layer you want from the map and its extent
  FeatureLayer lyr = m.FindLayers("GreatLakes").First() as FeatureLayer;
  Envelope lyrEnv = lyr.QueryExtent();

  //Set the map frame extent to the feature layer's extent / envelope
  mf_env.SetCamera(lyrEnv);  //Note - you could have also used the lyr as an overload option
});