Entire website is duplicated on 2 domains - what to do?

[BottleGreenWebsites]

My client's website has 1000+ pages and a Domain Authority of 23.

I have just discovered that the entire site is duplicated on a second domain (main URL = companyname.com - duplicate site URL = company-name.com).

The home page of the duplicate domain has a 301 redirect going to the main domain. However, none of the 1000+ other pages have any redirect set up, so Google is indexing the entire duplicate site. I'm assuming this is a bad thing for SEO.

Duplicate site has a domain Authority of 4, so I'd like to transfer whatever link juice it has, towards the main site.

What's the best thing to do?

Ultimately I think it would be best to delete the duplicate site. So would it be a case of adding a redirect to the htaccess file along the lines of:

redirect company-name.com/?slug? to https://companyname.com/?slug?    (I realise this isn't the correct syntax - but is the concept correct?)

Has anyone ever dealt with this successfully?

[AaronRainsSEO]

You are correct that you have to delete the duplicate website and set up in the redirects in the htaccess file. Once you have done that I would fetch the home page and other top-level pages to force Google to crawl. This will help with removing the duplicate pages out of Google's index.

Also, make sure they don't have a search console set up for the duplicate webiste with a submitted site map.