The General tab of the Modify DGN Export Setup dialog (see Exporting to DGN), includes the following panels:
If you want views placed on sheets or linked files in the project to be exported to a single file rather than to several files that reference each other, make sure the Export views on sheets and links as DGN references option is cleared. This setting establishes the default setting in the Export CAD Formats dialog when you export using this setup.
For the Export to file format option, select the desired MicroStation format from the drop-down list. The selected format will be the default format displayed in the Export CAD Formats dialog when you export using this setup.