Supplier Material for Purchase Order Line, How to add supplier's order number

Hello,

If we need some exterior operations from our suppliers, we are using Supplier material For Purchase Order Line module to ship and trace the material that our supplier needs.

After reserving the necessary parts, we are using “Print Pick List for Purchase Order” which creates a “Delivery Note for supply parts”. This is great to share the information with our supplier, but sometimes our supplier sends us a Purchase Order for the required material.

My question is how can I indicate our supplier’s PO number in the delivery note for supply parts ? 

Thank you for your help.

Baran