Hello,
You can copy content-product.php file (wp-content/themes/xstore/woocommerce) into child-theme/woocommerce folder and make changes there.
Also, etheme_product_countdown
(xstore/framework/woo.php) and etheme_countdown_shortcode
(xstore/framework/shortcodes/countdown.php) functions can be changed via functions.php file of child theme.
Regards