Hello,
1) Go to WooCommerce > Settings > Product tab > Inventory > enable Stock management.
Screenshot for Clarification: https://ibb.co/wsv1tn3
Next Edit the product > Inventory tab > enable stock and insert stock quantity.
Screenshot for Clarification: https://ibb.co/SVSRygG
2) Unfortunately, There is no option in Theme Settings available to meet up your requirement.
It requires customization and this is beyond our limitations and support policy.
3) Your screenshot doesn’t clarify your actual requirement please provide with relevant screenshot of the specific area from your website where you want to display the additional information to check it myself and help you out accordingly.
Best Regards.