COE# choose purchase order type when creating a PO

Hi community,

I tried to convert purchase contract to purchase order in the APP "manage purchase contracts". I chose the purchase contract, and clicked the button 'create purchase order', and the screen goes to 'manage purchase orders'. I need to choose the related purchase order type in the screen when I create the purchase order, but i can't find the field where i can do it. It will be NB purchase order type by default.... are there anyway that I can choose purchase order type?

Regards,

Shasha