How to I get "www." to show up on Google?? (WordPress website)

I’ve had the same domain name for over a year. I had an old basic site (HTML, not WordPress) for the past year. In the Google Results, my site would show the “www.domainname.com” which is what I liked.

I now have a WordPress website (which someone built for me), but the problem is in Google, it’s showing “domainname.com”

Now in google when I type in “site:www.domain.com” or “site:domainname.com” – the http://www.domain isnt showing anything.

I have verified BOTH website, but I am completely confused. I want the www. to be shown in Google

Thanks!