Trying to write an Assignment Rule that assigns a Change Task to the group in the Parent Change

Good afternoon, 

I'm trying to write an assignment rule that assigns a change task to the group listed in the parent change record via Javascript.

It works with:

var groupValue = "Tech Support";

I need it to pull whatever group is in the assign.dept field in the parent change, but i'm not sure what to use to make it search the parent record. Something like:

var groupValue = assign.dept in CurrentRecord;

Any advice would be greatly appreciated.