//Must be on QueuedTask
await QueuedTask.Run(() =>
{
// retrieve a map from the project based on the map name
MapProjectItem mpi = Project.Current.GetItems<MapProjectItem>()
.FirstOrDefault(m => m.Name.Equals("Your Map Name", StringComparison.CurrentCultureIgnoreCase));
Map map = mpi.GetMap();
//create a map page using map's default extent
presentation.AddMapPage(map, -1);
//create a page using map's bookmark
Bookmark bookmark = map.GetBookmarks().FirstOrDefault(
b => b.Name == "Your bookmark"); // get the bookmark based on the bookmark's name
presentation.AddMapPage(bookmark, -1);
});