Domain in server A Live site in server B setup help

Domain setup under develop in server A Live site in server B setup help

Hi,

I have a domain to server A
I want to create a new website for this domain and I want to setup in server B

Without nginx if you add under /etc/host of your machine the records of server B you could work website and when be ready change DNS

Now I have nginx and this cant work
In the past ( CPANEL ENGINTRON)
I did the following
if ($host ~ "localhost") {
set $PROXY_DOMAIN_OR_IP "127.0.0.1";
}

Now can I do that ? if yes where I can apply the code


Any help is welcome ?