Duplicated content from main page and index page

I hope I can make my question very clear but if I can't please be forgivable.

We have created a website and it called : www.website.com and with this website, it read the index.html file and therefore there will be this website: www.website.com/index.html. Obviously, these two will be the same with same content and everything.

My question here is how can I separate them. As in, when we audit the site, it keeps coming back as these two website are having duplicated content, duplicated title, and so on.

I tried to find an answer but I couldn't understand it myself so I couldn't find any question or answer related so if anyone could help that's be great.

Many thanks

I just want to let you know I fixed the problems, it's to add this code to .htaccess

RewriteEngine On
RewriteRule ^index\.html$ / [R=301,L]
RewriteRule ^(.*)/index\.html$ /$1/ [R=301,L]