Having re-read your post, I believe there to just be a misunderstanding of Navionics's confusing 'product line'.
If you bought the chart card for the plotter, this is entirely separate from their mobile app. To get charts on the phone
app, you then need to buy another subscription through the app.
If you would like to update the chart plotters data at any point within the year of its included updates, a relatively recent Lighthouse software
update (The Operating System of the Axiom line) supposedly added the capability of Navionics update/purchasing. I have not yet used it, but it should now be a feature nonetheless.
Firstly, you need to connect to the Display's own WiFi
Network. Doing so by: HOME->SETTINGS->THIS DISPLAY->WIFI CONNECTION SETTINGS-CONFIGURE->PASSPHRASE->SHOW CHARACTERS
You then connect your phone
to this network and open the navionics app. This should bring up some option to update the charts on the display permitting it is still in date.