I've found a solution:

1.  Move the charging station to the floor level you want to map and clean.

2.  Place the RV30 on the charging station.

3.  In the App, tap on maps.  At the top right corner of the window there's a plus (+) sign - tap the plus sign.  This will start the cautionary statements prior to mapping.

4.  Tap the button <start mapping>.

5.  When complete, the vacuum cleaner will return to the charging station.

6.  With the <Rooms> button on, tap the white start arrow (in a blue background) - this will start the cleaning process and update the mapping.

7.  When complete the vacuum cleaner will return to the charging station.

8.  Edit the floor plan name, name the rooms and merge/divide as necessary. 

9.  When next selecting maps, you can choose which floor map to use - make sure that the charging station is on the floor that you want to clean.

NB.  It's essential to have the charging station on the floor that you are mapping and cleaning.

Hope this helps others.

@Yusani 

@Wayne-TP The "do NOT move the charging dock" seems to contradict the instructions given by the app when adding a new floor map. It implies you need to move the charging station to ther new floor that needs to be mapped. 

After testing both ways, the moving of the dock (as suggested by the app) seems to work better. BUT the issue remains that beyond the mapping, unless you move the base everytime to the new floor for cleaning, at the end of the cleaning round the robot is lost.. it goes on endlessly searching for a base station that isn't there. As far as I can tell the product supports knowing of multiple floors, but it isn't designed to be able to move to a different floor, clean, and then stop where it started (without a base being present).