Note that only your U-admin can add teaching assistants to your course with different credentials. For example the following are the access rights your U-admin can assign to your teaching assistants. Note that teaching assistants by default does not have the credentials to make changes over student scores:
In this article you can find more details about the access rights for teaching assistants.
When you contact your U-admin to make a request (for example, you can create a support ticket here), please specify the access rights you want your teaching assistant to have.