Woocommerce took out the option for enabling a lightbox feature for your image gallery earlier this year. They have in their documentation to add code if you want to enable the gallery features but don’t actually say where.
https://woocommerce.wordpress.com/2017/02/28/adding-support-for-woocommerce-2-7s-new-gallery-feature-to-your-theme/
This is a significant frontend change that can be broken down in to three separate new features;
Image zoom / magnification
Lightbox
Slider
To enable each of these features in your theme you must declare support using
