Here we go ..
1. login to wix.com
2. edit your site
3. select the page where the app is installed or create a page and install the app
4. select the circle + add element feature
5. Select search
6. Search for 'Custom Code' then open it.
7. Add custom code to header section, name it 'Customer Reviews' and click apply
custom code '<script src="//writeacustomerreview.com/review/product_form.js"></script>'
8. Save and publish your site.
9. Test the code by appending ?&review_form=Y and navigate to products in your website if you multi-page enabled.
Example: https://www.leeacupuncture.biz/reviews?&review_form=Y