To Import Model(s) by Dragging from the Explorer Dialog

Open the Models dialog in the active model.
Open the Links tab of the Explorer dialog.
From the Explorer dialog, drag the required model(s) into the Models dialog.
Where one or more models in the selected file have the same name as existing models in the open DGN file, then an alert box gives you the option of overwriting the models in the active DGN, or renaming them automatically as they are imported.