If you created a TZ Cloud account and have TZ iBoat on your phone or an iPad and your 10X has access to an internet connection, you can take advantage of the synchronization to transfer the waypoints quickly and easily and create a permanent system to always save a backup copy of what's on your TZT 10X.
The trick is importing the waypoints to TZ iBoat, which is not totally obvious. The easiest way is to create the .gpx file with the waypoints you want to transfer, then send a text message with the file attached to yourself on your phone. If you have Tz iBoat on the phone, when you click on the .gpx file attachment to the message, it should be imported open in TZ iBoat. If it doesn't do that and tries to open in another app, just save the .gpx file to "Files". Then click on "Share" and choose iBoat as the default to open that type file.
Once you have the waypoints in TZ iBoat, all you have to do is log your 10X into your TZ Cloud account and it will automatically download and synch the waypoints.
Now in fact you can do it directly from a .gpx file on a USB stick as you tried to do with the SD card as Johhny notes You might try that first but setting up the cloud synch is a good idea either way.