How to reference Item EFF on Pricing Algorithm

Summary:

I'm customizing an Algorithm to be able to do tier base discounts using item EFF. I want to Sum all Qty from a spesific item EFF and apply a discount. I do have the steps to create the Algorithm but I'm not able to use (Reference) the item EFF

Content (required):

I define Item EFF on my Matrix Class

Item Extensible Attribute: AttributeGroupCode.AttributeCode: Discount Group.Discount Group.

How can I reference this into my Algorithm?

Said I created a Group Algorithm and under the "Group By Attribute" Section I want to use the item EFF.

What is the syntax?