www disappeared from website URL

Hi, I’ve installed the LiteSpeed Cache plugin on a WordPress site, but after this the “www” part in my website URL is disappeared. This is causing me a lot of SEO problems. Is there any configuration I can use to restore the www in the URL? Or there is something I can do on server side (i.e. editing the htaccess file) to restore it? I’ve tried to add www redirection on htaccess without results.
Thanks in advance.

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