I’d suggest you do the migration step-by-step. It is not related to license activation.
To activate your Verge3D copy, use the following procedure https://www.soft8soft.com/docs/manual/en/blender/Beginners-Guide.html#License_Key
To learn what version your devs used, launch the app, press F12 and switch to Console tab. There will be Verge3D version printed.
You can download the older Verge3D versions from this archive:
Verge3D Download Archive
If you do these steps, everything should work as before.
If you decide to do migration to newer versions, use the following guides: https://www.soft8soft.com/docs/manual/en/introduction/Updating.html
Verge3D versions are not always backward compatible so migration can break some features, and you will need to fix them by hand.