The WC single item template is located at:
yoursite.com/wp-content/plugins/woocommerce/templates/single-product.php
See this documentation:
https://docs.woocommerce.com/document/template-structure/
So, you would want to move any of those templates to your child theme under /wp-content/themes/your-child-theme/woocommerce/[any_template_you_want]
So, for example, if you wanted to edit the single-product.php but safe from WC updates, you would put the file in this directory and do your mods:
www.yoursite.com/wp-content/themes/your_child_theme/woocommerce/single-product.php
Last thing to mention here is keep the directory structure as well. So, if you want to edit something in the 'emails' folder, it would be like this:
www.yoursite.com/wp-content/themes/your_child_theme/woocommerce/emails/admin-new-order.php (just for example sake)
So, copy any templates you want to modify using that documentation above and you will be safe from any updates over time.