Use the Text & Fonts tab of the Modify DGN Export Setup dialog to map Revit text fonts to specific DGN text fonts.
Click File tab ExportOptions (Export Setups DGN). Select the setup to modify. Click the Text & Fonts tab.
By default, each Revit font listed in the mapping table has a value of {Automatically map font} in the Text Fonts in DGN column, which means the Revit font is maintained in the exported file.
To map a Revit font to a specific DGN text font, click the value for that font in the Text Fonts in DGN column, and select the desired font from the drop-down list.
To change all the values in the table back to {Automatically map font}, click Reset All.