Microsoft Bookings Changing your default domain when setting up Bookings mailbox

Question

We need to change the default domain name @abc.onmicrosoft.com on MS Bookings mailboxes with our custom domain name before creating the Bookings calendar. I am referring to this doc for more details, see section Changing your default domain when setting up Bookings mailbox, where it advises to change the default domain name for obvious reasons but does not mention any steps how to do that. Appreciate any help with actual steps on how to do change the domain prior to creating the Bookings calendar