Support, I'm trying to set up our server to use WP

Hi Support,

I'm trying to set up our server to use WP multisite combined with domain mapping to allow unique addresses as described in the docs.
We have a dedicated server which is now used for multiple (WP) domains.
I get that the IP should resolve to our multisite domain, but i can't seem to find how to change the server settings so that it will resolve to a domain iso the default server page.
Hope you can assist, Thanks