Sitemap can be helpful in pointing our crawler to webpages that are not internally linked within your website. When you add a new domain, we look for a sitemap at the root (e.g. www.website.com/sitemap.xml) of the domain and index all the links on the sitemap.
This guide explains how you can index a sitemap for your website collection.
...
Check if the sitemap exists on your website by going to www.yourwebsite.com/sitemap.xml. If sitemap is already present, skip to 3.
If sitemap is missing, then ask your website developer or technical team to add sitemap to your website.
Sitemap must be present at the root of domain and should be named "sitemap.xml" in order to be crawled (i.e. It can be located under any directory (e.g. www.yourwebsite.com/site/sitemap.xml).
Log in to your console and select the relevant collection.
Navigate to Domains section and click on "Diagnose".
Enter the URL of the sitemap, ie.eg. www.yourwebsite.com/sitemap.xml as the URL and press "Diagnose".
It would will return a message "Page not found in the index." Press "Add to Index".
...