SS3 - Open Roads - If I use the ‘Create From File’ command to import an InRoads DTM and I select ‘Import Features Only’ instead of Features and Terrain, How do I later create a Terrain model from within Open Roads?

If I use the ‘Create From File’command to import an InRoads DTM and I select ‘Import Features Only’ instead of Features and Terrain, How do I later create a Terrain model from within OpenRoads?