I would recommend getting familiar with the transformations in general. you see that the transformations are "stored" within the page types. So, you need to look for it in the Page types app. But how to know which page type to check? You can see it from the transformation code name. The default format is: <pageType.CodeName>.<Transformation.CodeName>
So, in your case the page type's code name is 'Ecommerce.Transformations' and transformation you are looking is 'Order_Address'