How do I update a specific value within array in a products metadata?

It’s a little bit off-topic, but nevertheless…

Let’s say you want to change first range_cost to 5.789 and third to 6.890 for product 148. Here’s the code:

$product_attr = get_post_meta( 148 , 'redq_day_ranges_cost');
$product_attr[0][0]['range_cost'] = 5.789;
$product_attr[0][2]['range_cost'] = 6.890;
update_post_meta(148, 'redq_day_ranges_cost', $product_attr);