Between the standard features in the goTenna Mesh user interface and those added by goTenna Plus, that functionality is already mostly built-in. I haven’t really tried mapping with it, but between the Location Tethering and the Trip Statistics features, they should be able to support you learning more about your goTenna Mesh location’s possible range. More here: https://www.gotenna.com/pages/gotenna-plus
Be aware, if you’ve not much experience, that small changes in location often result in a signal when one doesn’t seem readily apparent. One good way to test this is using the Ping feature, as it will work when the signal isn’t quite strong enough to support messaging. If the ping succeeds, try moving a little and you’ll often be able to connect for a message.
Also, you’ll find the iOS Toolkit available in the App Store has some neat mapping modes, although I haven’t tried it yet. More on it here: https://community.gotennamesh.com/t/ios-toolkit-app/1978