non-www & www

I installed WP Multi-site, and it suggested to list URL without the www. I have no problem with that. But, when entering www. before my domain it does not show my WP sites.

https://cpargolf.net works just fine.
https://www.cpargolf.net shows the main index.html page from my public_html folder.

How can I get the www. to work? Simply even if it is to redirect somehow to the non-www?

Thanks in advanced.