Hi Vitali,
is your post related to System Center Service Manager?
Service Manager has many User Roles, one of them being Administrators:
Manage Service Manager user roles
https://learn.microsoft.com/en-us/system-center/scsm/user-roles?view=sc-sm-2022
So, usually people enter groups for each role, so if you are able to find the group (maybe based on a OU or based on the group name) than you can gain control of the Installation. You might want to check also the local Admin group on the management server(s) as it is a requirement for the install, so it should contain the group or account you are looking for. You can reset the accoun'ts password then.
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Regards
Stoyan Chalakov