Not able to sort the PO numbers in descending order

Hi Team,

I am Rohit , I am new to ERPNext . I have created a custom doctype called " Stock Receipt" & i have created a link Field called Purchase Order & its linked with Purchase Order doctype.

I am able to see the list of PO in stock receipt but i want to achieve how to to sort the list in descending order .

Please find the screenshot ,

Regards