If you want an external developer to manage your account, they'll need to be added to your company's Workplace. As a best practice, we recommend providing third party developers with an email address within your company's domain.
To add a thirty party developer to Device Manager to manage your account:
From Device Manager, click People at the top.
Click Add People in the top right.
Click Find people by name and enter the person's name or email, then click on their name when it appears.
Under Assign Role, click next to Admin.
Click Invite.