Website Auditor identifies those. It’s the tool I use for all structure audits.
https://www.certifiedseo.com/audits
Depending on what platform the site is on, you would add a line of code to what’s called .htaccess file. It sits on the top of the server files. You add a line that looks like this:
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
The first line says “if this is not www” then the second line says to change it to www.
BE CAREFUL. Htaccess files can break your website if a single character is off.
If it’s a WordPress website, this plugin does it for free. 🤗
https://wordpress.org/plugins/really-simple-ssl/