NOTE: this guide is only relevant for those who installed the app through Shopify's app store!

You can use the products list page. Click on "View Products" from the dashboard

You should see this:

Then you can search in the search bar to find the product you want to check, then click into it.

Inside the product page, you can see a section for "Sizing Charts". Any size chart that matches with this product based on the product matching conditions will show up here.