To enter Private Notes on products, or specify custom Email Info, navigate to the product you want to manage, click edit, then click the Other tab.
Private Notes - Add private comments/notes for store admin users and click Post - ideal for fulfilment instructions or stock reminders.
Customers will not see these notes.
Email Info - Custom text field, which will be included in the order email. It could be a link to an online meeting or instructions for what to do next etc. Click Update to save changes.