set woo product fatured image by product first gallery image

index.php

<ul class="products">
	<?php
		$args = array(
         'post_type' => 'product',
			'posts_per_page' => -1
			);
		$loop = new WP_Query( $args );
		if ( $loop->have_posts() ) {
			while ( $loop->have_posts() ) : $loop->the_post();
            

         $product_id = get_the_ID();
         $product = new WC_product($product_id);
         $attachment_ids = $product->get_gallery_attachment_ids();

         echo $attachment_ids[0];
         echo wp_get_attachment_image($attachment_ids[0], 'thumbnail');
         echo '<br>';
     
         // if ( $attachment_ids[0] ) {
         //    set_post_thumbnail( get_the_ID(), $attachment_ids[0] );
         // }

			endwhile;
		} else {
			echo __( 'No products found' );
		}
		wp_reset_postdata();
	?>
</ul><!--/.products-->