Redirect to a URL without www

Whenever, i enter my site complete URL it is automatically redirected to my site URL without having www. I want the complete URL of my site should appear including the www in the start. Let me know which plugin i need to use for this purpose, thank you

Site link: https://w3torch.com/ 

No need for a plugin, this is a setting in the domains section of your website settings.

Go to Settings -> Domains click on your primary domain.

There's not really any advantage to having or not having the www. prefix, but changing it will impact your SEO negatively unless you update Google Search Console.