As a reseller, you have an app to submit under a client's Apple Developer Account to which they added you as Admin in order to perform the submission.
You would like to know if you can submit the article using your credentials, and if you have to submit any legal information concerning Intellectual Property.
If you are added as Admin on the client's Developer Account, you can submit the app using your credentials during the app publishing steps by ensuring the following conditions:
- You are able to receive the 2FA code, as explained in the Adding and Using a Trusted Phone Number for Two Factor Authentication (2FA) article.
- You must select the client's Apple/iTunes teams to avoid submitting the app under the ownership of your own developer account.
Concerning the requirement of any legal documentation by Apple, this will be under the discretion of the Apple reviewer. Please check our article on Apple binary rejected due to 4.2.6 and 5.2.1 guidelines for some guidance. Any documentation will need to be submitted to Apple directly as a response to their request.