You have to do that in sites-available and then create a symlink for it using sudo ln -s /etc/nginx/sites-available/subdomain /etc/nginx/sites-enabled/

server {
listen 80;
server_name usercontent.sportsapp.co.in http://www.usercontent.sportsapp.co.in;
location / {
proxy_pass http://localhost:3000;
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;
}
}

this is my sites-enabled/usercontent