I recommend you this great article from Moz.com about duplicate content:
https://moz.com/learn/seo/duplicate-content
How to fix duplicate content issues
Fixing duplicate content issues all comes down to the same central idea: specifying which of the duplicates is the "correct" one.
Whenever content on a site can be found at multiple URLs, it should be canonicalized for search engines. Let's go over the three main ways to do this: Using a 301 redirect to the correct URL, the rel=canonical attribute, or using the parameter handling tool in Google Search Console.
This is exactly what is happening on your site, if you check the source code of this page (with .html) :
https://www.dotmarket.eu/estimation.html
you will see this: <link rel="canonical" href="https://www.dotmarket.eu/estimation"/>
So that's the correct way to tell google and other search engines that the original contact for this page is hosted on that particular url (without .html)
Now please take in consideration that google is not reindexing the whole web every day! This process can take several days to several weeks to complete. You can speed up the process by providing your sitemap.xml file directly to google in google search console.