According to Logitech:
"24. I can't remember my login name/password, but I need to make changes. Can I upload my account from the remote, or do I need to start from scratch?
Unfortunately, you cannot upload the current settings from the remote. However, you may not be completely out of luck. At the login screen, select the "I forgot my password" option and say that you have the remote. Plug in the remote and it will be able to determine the username that was used to program the remote; write this down. Now request that the password be emailed to you and you should have the username and password to your account. Login to your account and you should find all your settings ready for you to make further adjustments. However, if for some reason you're unable to do so, you will have to start from scratch."
See this link: Harmony Remote FAQs
Based on reading FAQ 24, I'm guessing you might be able to plug in your Harmony 880, then indicate you have forgotten your password. At that point your password will be emailed somewhere???? Contact Logitech Tech Support to have the email sent to you, instead of the presumably WRV email that was used originally to set up your remote.