install filter

Hi,
Your snippet is to make the single product gallery images 250×250, but I don’t see that you have any single product gallery images on your product pages, so I assume that you was hoping this would do something else.

Nonetheless I added it to the end of your child theme functions.php file in Appearance ▸ Editor:

add_filter( 'woocommerce_get_image_size_gallery_thumbnail', function( $size ) {
return array(
'width' => 250,
'height' => 250,
'crop' => 1,
);
});

Perhaps this article will help you with what you are trying to achieve: How to override WooCommerce Image Sizes

Best regards,
Mike