How to make a site in forge "default" site

Hi, I have a aws ec2 server provisioned by forge and I have a site in that server lets say "site.com" now the thing is I have a custom domain feature in my site where it detects the tenant based on the domain that is accessing it. So for this I instruct my users to add a "A" record with the name "@" that points to the ip address of my server. But pointing to my server ip is not enough as it does not know which site to load because it determines it based on the domain accessing. so if my customers domain is "customdomain.com" my server will look for "customdomain.com" site which does not exists. How can I make my "site.com" the default site that should be loaded no matter what domain accesses it ?