Openstack Microstack : How to enable multidomain support for Horizon

I recently installed Microstack, Horizon dashboard is up. I wanted to test multi domain feature. I am not sure what config change is required for the same and in which file . I have looked at some places and they say, HORIZON_KEYSTONE_MULTIDOMAIN=‘TRUE’ will have to be added to /etc/horizon/ file .In my installation , I see a few of local_settings file , some in /snap/microstack and some in /var/snap/microstack directories.

Can you please suggest or point me to something which can be of help with this.
Thank you.