From WAS Admin console --> Global security --> configure
Provide LDAP server details and LDAP bind ID
Specify the base entry
Add group membership attribute
Above is just to add the federated repository, once this is done you should able to access the users/groups from this LDAP also . (But If you want to change the admin users then need to execute the wp-change-was-admin-user and change-portal-admin-user config tasks.