You can get it from the IDR applicant. An e-mail containing the Reference Number/Co-sign Code was sent to him or her. The IDR applicant can also access the Reference Number/Co-sign Code by logging in to StudentAid.gov and clicking on the appropriate link.
who should do the plan request when we log in?
The spouse of the applicant who initiated an Income-Driven Repayment Plan Request.
but I use their reference number since I don't have one, right?