Create a subdomain pointing to other sobdomain (in a external server)

You could add a CNAME entry to observatorio.* that points to funides.kingdatasolutions.com

On the destination server (funides.kingdatasolutions.com) you will need to add an entry for observatorio.funides.com to handle it properly.

Point observatorio.funides.com to your droplet and add the server block below to your NGINX configuration.

server {

  listen 80;
  listen 443;

  server_name observatorio.funides.com;

  location / {
    return 301 https://funides.kingdatasolutions.com$request_uri;
  }

}

Adjust this part of the entry return 301 https://f... to reflect if the destination is using SSL or not.