Link Sales order to WIP Job

We've a scenario where planner creates a WIP job manually (or release from ASCP) and once Sales orders are booked, they would want to manually associate the WIP job to the Sales orders. 

Once Discrete job is created, there is an option (button) for Sales order as can be seen on the form. However, I'm not able to associate an existing sales order to the WIP job.The LOV doesnt list the values and so,wondering if there is any program to be run

to populate the LOV values.