Below is an example of Generated Clusters before and after adding HLOD Volume.
HLOD Level Desired Bound Radius: 500
Drag in the Volume and scale accordingly to cover your Actors.
Selecting the generated LODActor from the HLOD Outliner shows the cluster created and the Cluster bounds.
Right-click on the LODActor in the HLOD Outliner and click on Select Contained Actors to see the Actors used for this particular LODActor in your scene.