You should take ownership of your app.
Use your Apple Developer account, and add your Developer as a member of your Team (with an appropriate role).
(If the app already exists under another account, then it will need to be transferred.)
Use your GitHub (or equivalent) source code repository, and add your Developer to that.
So everything is hosted/sourced on an account that you control.
Topic:
App Store Distribution & Marketing
SubTopic:
General
Tags: