After completing installation, click on the edit button
You will be notified to add code to .htaccess file. Click on the button add code to htaccess. If the extension does not find the .htaccess file in the server, the code will not be added and will give you warning message.
Go to settings tab and set all the required options and click on Save button
You are done. The XML sitemap files will be shown in your dahboard tab of this extension
Once everything is fine, you can submit the sitemap index file to google search console (google webmaster)