You can ping Google by sending a GET request in your browser or the command line to the following address. Make sure to put the full URL of the sitemap.
https ://www.google.com/ping?sitemap=FULL_URL_OF_SITEMAP
E.g.
https ://www.google.com/ping?sitemap=https ://qa.tellustheanswer.com/sitemap.xml
(Remove the space between "https" and ":" in the above ping URL. )