How to configure Nginx to distinguish between PC or mobile phone access to different domain names

server {
  listen 80;
  server_name www.7d.com 7d.com; // New official website domain name rewrite .* https://$host$request_uri last;
}

server {
  listen 443 ssl;
  server_name www.7d.com 7d.com; // New official website domain name root /data/7d;
  charset utf-8;
  ssl_certificate /usr/local/nginx/_.7d.com.crt;
  ssl_certificate_key /usr/local/nginx/_.7d.com.key;

  rewrite /s1$ http://s1.7d.com/start last;

  if ( $http_user_agent ~* "(Android|iPhone|Windows Phone|UC|Kindle)" ){ // Redirect judgment rewrite ^/(.*)$ https://m.7d.com$uri redirect; // redirect means 302 redirect (temporary transfer)　
  }   
  …
}

 server {
  listen 80;
  server_name m.7d.com; // old official website domain name rewrite .* https://$host$request_uri last;
}

server {
  listen 443 ssl;
  server_name m.7d.com; // old official website domain name root /data/7d;
  charset utf-8;
  ssl_certificate /usr/local/nginx/_.7d.com.crt;
  ssl_certificate_key /usr/local/nginx/_.7d.com.key;

  rewrite /s1$ http://s1.7d.com/start last;

  if ( $http_user_agent !~* "(Android|iPhone|Windows Phone|UC|Kindle)" ){ // Add a ! before ~. If it is not accessed from a mobile device, it will jump back to the new official website.
    rewrite ^/(.*)$ https://m.7d.com$uri redirect; // redirect means 302 redirect}   
  …
}