"301 redirect" Been discussed before but I would like to do it correctly for my site.

WebSiteGrader Gave this error for SEO

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Permanent Redirect Not Found

Search engines may think www.mysite.com and mysite.com are two different sites.You should set up a permanent redirect (technically called a "301 redirect") between these sites. Once you do that, you will get full search engine credit for your work on these sites.

For example, www.mysite.com seems to have 57 inbound links whereas mysite.com has 61 inbound links. By correctly configuring a permanent 301 redirect, the search rankings might improve as all inbound links are correctly counted for the website.
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my drupal is in / not in any folder or etc.

What would be the correct way for my case...

Thanks for your feedback in advance.