Before you can use Cross Sell, you'll need to add one line of liquid code to your theme's product and cart templates (cross sells will NOT show if this is not done).
This will only take a few minutes, and we can help you do it if you are not sure how to proceed.
Can you install Cross Sell yourself?
* if you're using a page builder app like GEMpages, follow these steps to add our liquid snippet: https://intercom.help/gempages/faqs/how-to-embed-custom-code-with-liquid-element
** if you're using Shogun to build templates, please create a custom liquid element with these instructions: https://getshogun.com/help/en/articles/1391680-creating-custom-elements-with-liquid-css-and-js and then embed our snippet to the end of your product template