add line breaks at customer details on thank you page

It should already be broken up in multiple lines. Your theme likely has some css preventing it.

Try temporarily switching back to the WordPress Twenty Sixteen Theme, or Storefront, and disable all plugins except for WooCommerce. If that resolves the issue, then slowly re-enable features until you find the one that’s causing the conflict.

If you find your theme to be the problem, you should contact the theme authors.

thanks caleb. which file is listing this info. i checked the thank-you page but it’s not showing up there?

This is what it looks like w/ the Storefront theme: https://cld.wthms.co/1eRKe/4aHkF0U0

Your theme must have removed the default WooCommerce styling, and the authors forgot / never got around to styling this section. You need to contact the theme authors.

Are you asking what template is being used? Here it is if so: https://github.com/woothemes/woocommerce/blob/master/templates/order/order-details-customer.php