```
/* gallery image size change in single product page */

add_filter( 'woocommerce_gallery_thumbnail_size', function( $size ) {
  return 'full'; // ‘full’ , ‘thumbnail’, ‘medium’, ‘large’
});
```
For more details please click [enter link description here][1]


  [1]: https://woocommerce.com/document/image-sizes-theme-developers/