Hi @cbzhu
Thank you for posting in the community!
If the product description is available in your product catalog, you can use the catalog lookup to showcase it in your flow mails with the below setup:
{% catalog event.ProductID %} {{ catalog_item.description }} {% endcatalog %}
Usually it comes with some formatting, but using either the |striptags or |safe, you can remove these depending on the styling of the description on your site.
Remember that the {% catalog event.ProductID %} can be unique to your integration, so when you have inserted it into your email, please check if event.ProductID corresponds to your preview variables :-)
You can read more here: https://help.klaviyo.com/hc/en-us/articles/360004785571
I hope this helps!