At this moment, there is no API available to log out Managed Accounts and reset all their sessions. 

Suggestion

Release an API endpoint for the Organizations REST API that allows Org Admins to reset their Managed Account's sessions. 

Workaround: 

It's possible to reset the users' sessions manually from the Authentication Policies, as mentioned in the following documentation page: 

• Reset sessions

It's also recommended to adjust the idle session duration to a lower value to ensure the users are logged out periodically if they remain inactive for too long:

• Update idle session duration

However, with this approach, it's not possible to exclude some users. Hence, all users assigned to the Authentication Policy will have their sessions reset.