Convert Sales quote to Sales order 2020

Hello everyone,

When using the "Convert Sales Quote to Sales Order" function, the "Order No." field in the " Sales Order"  automatically gets populated with the quote number.

Therefore when we want to change the order number to our customers' PO number we are blocked and cannot complete the task without making a new sales order.

Once a sales quote gets converted where are we suppose to insert our customer's PO? 

Using the message field for this is not ideal nor professional.