Grant service user of client permission to manage only its own client

I would assign the service user of a client the right to edit his own client (e.g. set the backchannel redirect url, as well as edit the valid redirect urls).
I have already enabled the preview feature “fine grained permissions” using “keycloak.profile.feature.admin_fine_grained_authz=enabled”. How do I add the permission to the service user?