How to change an Object Acct using OT Change rule?

I have a Change Rule set up that changes Regular Pay (PDBA = 1) to OT pay (PDBA = 120).  In this same Change rule, when I set the PDBA to 120, I also set OBJ to 3130.  However, the OBJ is not changing.  I found info that says to "set MCU, OBJ and ANI to blanks first".  However, ANI is not available as a field in the Change Rule.  Has anyone had this problem?  How do I get the OBJ to change to the correct Obj Acct according to the AAI's?

Thanks,
Margaret