It's a custom theme, so first of all you should check if WooCommerce support is declared in the functions.php. Woocommerce Integration with theme can be done using declaration of support in the theme. Php code:
function wpse319485_add_woocommerce_support() {
add_theme_support( 'woocommerce' );
}
add_action( 'after_setup_theme', 'wpse319485_add_woocommerce_support' );
link:https://github.com/woocommerce/woocommerce/wiki/Declaring-WooCommerce-support-in-themes