Search for Enterprise Item Number as a attribute.

We are using Enterprise Item Number (EIN) in our cloud. I can search for the number.
But in the 6WTags it is not an option. How do I configure the 6wtags to get EIN as a filtering option?
When I use advanced search the issue is the same. I select Physical Product as a Type, but the EIN
is not a option. How do I configure that ?