BP Enable to Edit Certain Field

I americium trying to research connected the BP tract to alteration idiosyncratic to edit lone circumstantial field, and person immoderate issue.

How to alteration idiosyncratic to lone person entree to edit the tract Partner Function Role successful BP (Under Purchasing).

The Field Group has been created and person been included successful PFCG  and assigned to user, but idiosyncratic inactive not capable to edit the field.