How to config nginx for multiple nodejs apps?

i just config nginx like this

  server {
    listen 80;
    server_name mydomain.com www.mydomain.com;
    location / {
      proxy_pass http://167.172.192.169:7000;
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection 'upgrade';
      proxy_set_header Host $host;
      proxy_cache_bypass $http_upgrade;
    }
  }
server {
  listen 80;
  server_name app.mydomain.com;
  location / {
    proxy_pass http://167.172.192.169:38453;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
  }
}

i want sudomain app run in other node app but i still get stuck here, did i need config and DNS ??? pls help