How do you reference a collection/group in Database Service and Action menus

I have a query that uses the 'where {column} in' clause.  I need to reference a result stored in a control  from another section of the form.  I expect that this result could have more than 1 item.  So how do I reference these items in Action section.  

In other words I've successfully created queries with params and multiple params.....but these have a single value (not a collection) being referenced.  How can I reference a control that is a collection?

Thanks for your help