Hierarchical LOD - Automatic Workflow

Open World Settings tab Window / World Settings.

Enable Hierarchical LODSystem. Window / Hierarchical LODSystem / Enabled Hierarchical LOD System

Open Hierarchical LOD Outliner Window . Window / Hierarchical LOD Outliner

Add Levels.

Update clustering settings.

Enable Simplygon Proxy Mesh Generation

Generate Clusters

Generate Proxy Meshes for Cluster