The website might have been indexed because it contains duplicate content from another website that is indexed. This happens if the dummy website is using a template or content that is also used on another website.
To remove a dummy website from search engines, you follow these steps:
The robots.txt file is a text file that tells search engines which pages on your website they should index. If the dummy website is not listed in the robots.txt file, then search engines will be able to index it. To prevent indexing, you add the URL of the dummy website to the robots.txt file.
Add a no-index meta tag. The index meta tag is a tag that tells search engines not to index a particular page. You add the no-index meta tag to the <head> section of the dummy website’s HTML code.
Submit a request to Google to remove the dummy website from their index. You submit a request to Google to remove the dummy website from their index using the Google Search Console.