If you have a @un.org email account, the preferred method is this: click the “Login using Identity Provider” link as shown in the screenshot above. It will lead you to the usual United Nations logging in page. Enter your UN email and the password you use to log in for UniteID (iseek, umoja, web outlook, etc).
Contact the administrator to approve your account and wait for your account to be approved. Your account will work only after it is approved.