Overland Navigator allows you to upload your own tracks via GPX files.
To do so, first make sure you're signed in to the web application at https://overlandnavigator.co.nz/ - be sure to use the same login that you use on your phone.
If you use an iPhone you can also record routes right in the app. Find out how.
Click the 'Add' button on the main menu
Click 'Add' under the track title
Click 'Choose GPX' and pick your GPX file - if it's valid it will be drawn on the map and the map will zoom in. Press next when you're done.
Supply some basic details about the route - the next button will light up green when ready.
Done!
Next time you open the app on your phone the track will appear. Behind the scenes Overland Navigator works its magic to populate any missing data and clean up any strangeness that can come from recording routes.