Form field default value from list lookup

This should be possible, but I suspect it would require javascript rather than just inline functions. On a Nintex Office 365 form, I need to set a default value for a person field from a list lookup if the value on another field meets certain conditions.  This is at the Form level, rather than within Workflow.

Requirement:

If Division_field = {X} and Location_field = {Y}  (first couple of fields filled out by user)

     then set default value of Manager2_field (at bottom of form) to be Manager2 field value from Manager2_List where Location = {Y}.

Else

      default is blank.

Any suggestions or pointers would be very much appreciated.  I haven't done much coding with javascript in this environment so any javascript solutions would need to be verbose.

Thanks!