How to remove Missed Call Notification on Yealink T48U

I have read the feed for "How to remove Missed Call Notification on Yealink T48S" but we are having the same issue on the T48U. Specifically, my issue is that default admin user name and password. Again, there have been feeds for default passwords on here but those have not worked for me. Even looking on the web, I cannot find a way to gain access to the phones to disable miss call notifications. Please help me.