By default, our crawler is looking for the sitemap.xml in the root folder (domain.com/sitemap.xml), If your sitemap is located elsewhere or has a different name you can add its URL to the settings so the crawler will follow it.
You'll find this option in the Project Settings -> Advanced Crawl
You can add as many sitemaps as needed.(one per line)
If your sitemap_index.xml is not recognized correctly please add each sitemaps URL from the index.