This tool supports only HTML file downloaded from the Google SERP. In order to extract URLs you will need to load all your indexed pages of the website into one page on Google and just save it as an HTML file and upload it here.
Click process button and in a few seconds you will get the list of all URLs that were on that SERP page. You can use this SERP URL extractor for free. This tool can save you time to manually extract all indexed pages of specific website on Google, as sometimes pages in the sitemap and Google Search console can vary compared to indexed pages on Google.
This tool can help you to map your 301 redirects better and cover all indexed pages of your website during a website redesign or migration to another domain. Make sure that in order to get proper Google SERP links extracted to upload an HTML file only. To achieve that just right click on SERP and save it as an HTML file.