public void Planarize( 
   Layer layer,
   IEnumerable<long> oids,
   Nullable<double> clusterTolerance
)

// note - EditOperation.Planarize requires a standard license. 
//  An exception will be thrown if Pro is running under a basic license. 

var planarizeFeatures = new EditOperation();
planarizeFeatures.Name = "Planarize Features";

//Planarize one or more features
planarizeFeatures.Planarize(featureLayer, new List<long>() { oid });

//Execute to execute the operation
//Must be called within QueuedTask.Run
planarizeFeatures.Execute();

//or use async flavor
//await planarizeFeatures.ExecuteAsync();