Hello eltabei,

Hope you are doing Well.

For adding the ribbon on product, you will need to go to the product in debug mode. Then you will have to go
to the ecommerce tab where you will find the ribbon field from where you select the sale ribbon.
After which the ribbon will be visible on the product.

You can refer to the youtube link: https://www.youtube.com/watch?v=1miSwZVQwF8

I hope it will help.

Thanks & Regards,
Email: odoo@aktivsoftware.com
Skype: kalpeshmaheshwari