This is a very common problem and can be described as being an issue with 'canonicalisation'. Essentially, you only want to show one (or canonical) version of your web content to search bots as opposed to multiple versions across varieties of URLs e.g. www.domain.com, domain.com, https://domain.com etc.

This problem can be solved in a selection of ways:

Canonical tag - use the canonical link element referencing the preferred URL.

Permanent redirects - use a 301 redirect to the preferred URL.

Set your preferred domain in Google Search Console - this is the easiest, due to the lack of dev time required and seems to suit your specific issue.