Perhaps you could be a bit more specific about the problem?

It seems to use an app to control the unit so I'd imagine the first step is to transfer the route into the app.

Can you do that? 

If so, it may be a matter of trying which format is better for the app/unit. As well as gpx formats there are different types of tcx as well. 

I'd imagine your best course of action is to search for Nyon support or groups on Google groups. Now that I think of it I found https://www.bosch-ebike.com/en/help-center/how-do-i-import-existing-gpx-routes-into-the-ebike-186626

Good luck! 

Steve,

I have created routes using cycle.travel and imported them onto the Nyon via Bosch eBike Connect on a laptop. Works fine however it is specific about using gpx track. You normally get a warning on the Bosch website about the route matching known roads on the Bosch map. I have ridden routes using the Nyon and my normal GPS unit to compare the two. I have now abandoned the Nyon for navigation purposes. The interface is poor and it missed a couple of turns compared to my GPS unit. Might be something to do with the Bosch using gpx and the GPS using tcx. It means mounting an extra unit on the bars but it is well worth it! Hope this helps. Ray.

Steve,

Forgot to mention Komoot. Not my favourite option, but it works. Sync Bosch and Komoot. Create route on cycle.travel, export .tcx, import to Komoot. Voila! Ray.

Thanks for your help. I'll have a play this weekend.