The products single page is generated by the Woocommerce plugin and to change things around and customize that page you need to override the PHP file in your Child Theme.
That customization is outside of our support scope but you can continue learning about it here:
Also, this Google Search will help you get started.
For more information on how to customize the theme itself I suggest that you read the article below:
And finally, you can use the Cornerstone to customize the description section of the product by going to X > Cornerstone and adding the Product post type there and click the update button at the right section of the screen.:
Then you will have the option available for each Product edit page: