Not sure why the original discussion was closed.
The answer marked as best (Walter ...) was not an answer. In spite of what he said, the app did not work on the course I played.
So the question is still
How to combine the 2 9-hole scores so they show up as a single 18-hole round.
In looking at some past support tickets generated on the subject here's the reply from the team:
"Unfortunately, you can't combine it in a simple way. But you can manually input shots from the second nine. To do this, please open your "Playing history", then "View&Edit" -> "Round settings" and "Change course".