nginx - how to redirect child domains to specific localhost ports in windows server 2008 VPS?

I have a VPS which is running Windows server 2008 datacenter with one Static IP address.

I can access from Internet to my web services by specific port e.g mydomain.com:3000/api and mydomain.com:4000/api. I want to change this web services access address into sub domain method (child) like App1WS.mydomain.com/api and App2WS.mydomain.com/api

update

I add this line to host file

127.0.0.1      mobileapp.myrealdomain.com

Then in nginx, I add these lines at the end

 server {

        listen       80;
        #root html;
        root c:/apps/web;
        server_name  mobileapp.myrealdomain.com;
       location / {
           proxy_pass  "http://127.0.0.1:3000";
        }
}

Then I started my loopback project which is accessible via:

C:\apps\mobileapp>node .
Web server listening at: http://localhost:3000
Browse your REST API at http://localhost:3000/explorer

Then I've add Alias(CNMAE) record to DNS:

alias name: mobileapp

FQDN: mobileapp.myrealdomain.com
FQDN for target host: 127.0.0.1:3000.

From other location on Internet myrealdomain.com loads homepage but still mobileapp.myrealdomain.com showing

server DNS address could not be found.

In VPS mobileapp.myrealdomain.com works properly and loads server up time

{"started":"2017-09-23T10:29:30.626Z","uptime":48.709}