Thanks for writing in! Customizations are fall beyond our scope of the support and we can only provide some guidance for certain customizations.
For this type of customization, first you need to setup a child theme and activate it by following our guide here (https://theme.co/apex/forum/t/setup-how-to-setup-child-themes/57).
Then you can copy the file
single-product-reviews.php under "/wp-content/plugins/woocommerce/templates/" into your child theme
Then search for the following CSS class
woocommerce-Reviews-title that have been applied into a H2 Tag and change it accordingly.
Hope that helps.