How to reset Data Reference type of Event Frame's attribute to "None"?

Discussion created by susan on Feb 19, 2014
Latest reply on Feb 19, 2014 by Marcos Vainer Loeff

I want to rewrite one event frame attribute's history value in 2013. This data reference of this attribute was formula, so I think I have to reset to "None" in order to call UpdateValue. but I cannot find how to do it? thanks!