Taxpayers do not use ProConnect Tax, tax professionals do.

If whoever you are helping is a ProConnect Tax user and have sent you an invite under his account, you should will see all the returns he has permitted you to see.  If not, he may have limited your access and/or role.

You can refer to this article and work with the firm's owner to sort that out:

https://proconnect.intuit.com/community/manage-access/help/how-to-manage-user-permissions-and-invite...