What you're asking is impossible. DNS only maps domain names to IP addresses, like to allow a browser to find the web server (or to allow email software to find the target SMTP server, and so on). Next, the browser will tell the server for which domain it wants the web site; see What exactly happens when you browse a website in your browser?
Likewise, you cannot map some specific URL to another server, or map a domain to a specific port.
If your web server needs to handle requests for multiple domains, you need something called "virtual hosting", to map domains to folders. If you only have one domain, you somehow need to tell your web server to set the root of the website to the specific folder.