To Start Indexing in DGN Indexer

Open the Explorer Settings dialog ( File > Settings > User > Explorer Settings ).
In the Explorer Settings dialog, click the icon in the Indexing Service row.
The DGN Indexing Options dialog opens.
In the Locations tab, in the Change selected locations list box, click the arrow next to the drive to expand the drive.
Select the folder(s).
The folder(s) appear in the Summary of selected locations list box. The Items Indexed field in the Index settings tab displays the number of items indexed.