The best way to handle this would be to add the developer (perhaps temporarily) to the Zoom account that you’re developing the app under. This way, they’ll be able to create or manage the app, as well as authorize for testing purposes.
Note that if a developer belongs to a separate account than the app itself, they won’t be able to authorize it locally. It will only be possible to install the app externally once the app is reviewed and approved by Zoom.