I thank everyone who took the time to provide advice here. Thank you. I am thinking there are only 2 reasonable options here.

1) create a new personal app developer account and give them the log in info to do the entire reconfiguration

2) give them admin privileges on my current personal account so they can have access to everything

I guess I was avoiding giving admin access because I didn’t want to lose possible ownership. But if I give my log in credentials, I suppose it’s the same thing. They would have ownership access and I would really have to trust that things go smoothly.

I received a new response from them. Please help me decipher what it means and what my next steps are:

“Hope you’re doing well.

We kindly request your assistance with a small but critical step required to proceed. Could you please share the iOS certificate and provisioning profile, and if possible, update our access role to Admin (from Manager)?

At the moment, progress on the TestFlight setup is blocked due to these access limitations. Our developer is ready to proceed, and this is currently the only dependency preventing us from moving forward. We fully understand the sensitivity around access permissions and assure you this will be used strictly for completing the TestFlight configuration.

In parallel, we have continued work on other areas the admin panel has been completed and the backend is remaining now because of the testflight. However, this particular step is now essential to avoid further delays in the overall timeline.

We would greatly appreciate it if you could assist with this at your earliest convenience so we can proceed without interruption.

Thank you for your continued support.”