How to add onChange event in a field in header - Dynamics CRM online?

I am working on a Dynamics CRM Online form. There is a Status Reason field in the header. I want add onChange event for this field.  

1. In the Form Properties editor window, header's controls are not visible in the control selection for adding event handlers.

2. Then I tries to use addOnChange method, I got errors "addOnChange" is invalid. 

    Xrm.Page.getAttribute("header_statuscode").addOnChange(ChangeStatusReason);

Thanks for reading my question, I appreciate your time for answering.

Runner288