Unfortunately, it's not easy. Google has been steadily locking down permissions to access app-storage outside of apps (including taking away "external" storage for non-approved data types, anything other than documents and images) in more recent Android.
There's an open "Issue" for it on github
https://github.com/wiglenet/wigle-wifi- ... issues/450, but how we'd do it is ill-defined, since the databases get large (too large even for most folks' Google drive allocation), and we'd need to reconcile incoming data with existing data. Depending on whether you upload the data to the site, you CAN import from the uploads activity, but there's nothing "batch" about this - you'd have to import upload by upload (and you wouldn't get every observation).
From a scanning note: it's almost better NOT to import the old database; more effective to keep it on your laptop/desktop/server and access it there. As the database gets bigger, Android has more and more trouble accessing if efficiently; this results in degraded app performance as well as slower/less-reliable scanning and logging.
Cheers,
-Ark and the WiGLE team