This updates all Media Files in your WooCommerce / WordPress site with an alt tag. First it updates alt tags by product parent assigned title, then it updates media with product based query and in the end it takes media title.

Update WooCommerce & WP Images with Alt Tags Automatically

<?php

$updatedImageIds = array();
$productsUpdated = array();

//////////////////////////
// Update Images where 
// post is assigned
//////////////////////////
$parent_images_args = array(
    'post_type'      => 'attachment',
    'post_mime_type' => 'image',
    'post_status'    => 'inherit',
    'posts_per_page' => -1,
);

$parent_images = get_posts( $parent_images_args );
foreach ($parent_images as $parent_image) {

	if(!isset($parent_image->post_parent) || empty($parent_image->post_parent)) {
		continue;
	}
	$parent_id = $parent_image->post_parent;
	$productsUpdated[] = $parent_id;
	$parent_title = get_the_title($parent_id);

	$image_id = $parent_image->ID;

	$updatedImageIds[] = $image_id;
	update_post_meta($image_id, '_wp_attachment_image_alt', $parent_title);
}

//////////////////////////
// Update Images by Looping
// through products
//////////////////////////
$products_query = array(
    'post_type'      => 'product',
    'posts_per_page' => -1,
    'post__not_in' => $productsUpdated

);
$products = get_posts($products_query);

foreach ($products as $product) {
	$product_name = str_replace(array('..', '...'), '', $product->post_title);
	$product_image_id = get_post_thumbnail_id($product->ID);

	if(!empty($product_image_id) && !in_array($product_image_id, $updatedImageIds)) {
		$updatedImageIds[] = $product_image_id;
		update_post_meta($product_image_id, '_wp_attachment_image_alt', $product_name);
	}

	$product_gallery_images = get_post_meta($product_image_id, '_product_image_gallery', true);
	if($product_gallery_images) {

		$product_gallery_images = explode(',', $product_gallery_images);
		$i = 1;
		foreach ($product_gallery_images as $product_gallery_image) {

			if(in_array($product_gallery_image, $updatedImageIds)) {
				continue;
			}
			
			$updatedImageIds[] = $product_gallery_image;
			update_post_meta($product_gallery_image, '_wp_attachment_image_alt', $product_name . ' – Detailbild ' . $i);
			$i++;

		}
	}
}

//////////////////////////
// Update restly images
//////////////////////////
$other_images_args = array(
    'post_type'      => 'attachment',
    'post_mime_type' => 'image',
    'post_status'    => 'inherit',
    'posts_per_page' => -1,
    'post__not_in'   => $updatedImageIds,
);
$other_images = get_posts( $other_images_args );
foreach ($other_images as $other_image) {

	$other_image_id = $other_image->ID;
	$other_image_title = get_the_title($other_image_id);
	$new_image_alt = str_replace(array('-', '.'), ' ', $other_image_title);

	update_post_meta($other_image_id, '_wp_attachment_image_alt', $new_image_alt);
}