You can do this with a redirect. To set up a redirect, perform the following steps:
1. Log in to your old site's cPanel interface.
2. Navigate to cPanel's Redirects interface (Home >> Domains >> Redirects).
3. Set the old site's index page to redirect to the new site's index page.
If you want the old site and the new site to go to the same location, but you have not yet set up the new site, you can use aliases. An alias allows you to add a second domain name to your account that goes to the same website.