SAP CS ( How to cancel the Service order)

Hi Experts,

Scenario: Return sales order is created which triggers a Service order. here we carry out internal or external repair( repair to Vendor).

Now we need to cancel the Return sales order and it can be cancelled only when the subsequent document ( Service order) is cancelled.

So please let me know is it possible to cancel Service order? if yes please let me know the procedure so that we can cancel return sale order( or reject line item in RSO )

Note: The Service order is already processed (Partially confirmed, Goods movement posted, Pre-costed, Return, Settlement rule created)

Thanks in advance,

Ali