List of all Master admin users

is there way to list all Master admin users on the system

Things happened that debian server had inherited by me in the firm without any information. And I need manage things with that. I found out dozens of Virtualmin users, but they all are “Server owners”. If I connect with root I get very poor window without any possibility to make changes, only information about system. So I need to find Master admin users then I will just change password…


please post a screenshot of the window shown after logging in with root

Thank you for your reply maznos.
Here screenshot of root login: