Note - It takes couple of hours to activate the custom domain. Contact firstname.lastname@example.org for any issues activating custom domain.
To set up the DNS redirect for the root domain (like user going to https://mydomain.com) the CNAME entry in the DNS setting will be CNAME with @ (for root) and the target will be your sub-domain within https://ngage.ai. See the screenshot below.
The entry for root domain