See here for detailed instructions on how to activate your HHU alumni account.
If you still know your university identifier, you can use this to activate your HHU alumni account on idm.hhu.de. First, click on “Alumni-Anmeldung” (alumni registration) in the menu on the left-hand side.
Then select a role for your network membership under “Beziehungen” (relationships). This is usually your role as a student. Your new status should now appear in the “Alumni-Beziehungen” (alumni relationships) field. You can change this at any time later on.
Once your new status has appeared in the “Alumni-Beziehungen” (alumni relationships) field, click on “gespeicherte Adresse übernehmen” (use saved address) to confirm your address. If you have since moved house, you can change your address manually.
Re-enter your email address if this has not been displayed automatically and click on the check box to confirm that you wish to become a member of the alumni network. Finally, click on “Zustimmen” (agree) to complete your registration.