Any adding/blocking/removing from Active Directory will have to be done by the admin of the AD domain. Tableau Server has read-only access to the domain and asks the domain for all authentication without storing any information. I.e. Tableau Server cannot make any changes to the directory.
I hope this helps!
You should disable the account at Active Directory or incase you would need to do it tableau level, you can remove the user from the group, but this is a not a best approach as you should always use Active Directory to manage user and tableau just pulls from the AD group and imports the users.