Open Fly example scene and specify Bing Maps API Key in Bing Maps Elevation Manager.

P.S. Soon or already Bing Maps should close its mapping services.
You can replace Bing Maps Elevation Manager to Mapbox Elevation Manager.

In the demo video and one of the pics shows a plane flying over a map section with relief (pic attached).

Which example scene demonstrates this?   I've checked all the example scenes and the atlas of samples seems to be limited to sampling elevation at a single point.