Having both www and non-www being allowed isn’t good practice.
You can get dinged for duplicate content so your page’s SERP ranking can get hurt.
You see https://www.example.com and HTTP://example.com can be two totally different sites running on two different servers in different parts of the world. So example.com is the domain name and www is considered a subdomain of example.com.
First, you need to pick the survivor you want to keep. Looks like you registered one with www, but search engines are pointing to the other. If it’s not difficult to change the registration, I’d keep what search engines are using or you might take a hit, but it’s up to you. You might have advertised with one or the other.
Once you choose the one you want to keep www or non-www then you need to redirect to the one you want to keep.
If you are using Apache then you can have a look here.