Purchase order type not defaulting.

Purchase bid benignant not defaulting erstwhile converting it from Purchase requisition that's driven by MRP.

I'm trying to person the Purch Requisition to a circumstantial Purchase bid (STO bid type), but the strategy is picking immoderate random PO Doc type. 

How bash I marque the PO Doc benignant default for a circumstantial Purchase Requisiiton?

Appreciated your help.