vRealize Operations 6 is major change from 5.x version. It is an architecture change. The root password is no longer set as part of installation. Quoting the manual “After you install vRealize Operations Manager, you secure the console of each node in the cluster by logging in for the first time. ”
To set it, you have to go to the console (I have not figured out how to do it on Windows as to me it’s easier to use appliance). So launch the console. I use the vCenter C# sharp client below.
Press Alt+F1 to get the login prompt. Type root. The default password is blank, so you simply press Enter key. It will prompt you to change password. Type the new password. It checks for password complexity.
Once done, you get the screen below.