You can add google remarketing code on any page of your ecommerce site. To add google remarketing code on your e-commerce site, go to any page of your site through design theme. Following are the steps:
Here, you will need to modify the provided code according to the code which you get from Google AdWords. To know more about design theme, visit the helpcenter - https://help.storehippo.com/topic/how-to-add-google-remarketing-code-on-site