To add a new attribute at the level of a specific product manually, follow the instructions below:
In your store's Admin area, find the product you want to add a new attribute for, open its details, and click on the "Attributes" tab.
A page where you can manage attributes for this product will open. Here you can see three subsections:
Make sure you are viewing the "Product-Specific" section.
If you haven't added any product-specific attributes for this product yet, the Product-Specific attributes list will be empty:
Use the "Add attribute" button to add a field for the new attribute. There you will specify your attribute name and value(s).
The "Add attribute" drop-down will give you a choice of three types of attribute value fields:
Select the type that best suits your needs (More details on the different attribute value field types, see in Attribute Value Field Types).
By default, clicking the "Add attribute" button creates a "Plain field" attribute. To select a different field type, click on the "down arrow" expandable part of the "Add attribute" button and choose the type you require from the drop-down button menu:
A new attribute field will appear on a new line in the Product-Specific attributes list.
For the sake of example, the snapshot below demonstrates a newly added Plain field:
Use the newly-added field to specify your attribute's name and value (or, if necessary, multiple values). For the sake of example, we will create the attribute "Rim color" with the value "Black":
Click "Save changes." The attribute will be assigned to the product.
Now, if you check the "Specification" tab on the product details page, you will be able to see the attribute you have added there along with the product SKU and weight that are present there by default: