how to un apply to return line ??

hi All , i have created a sales order and pick, shipment even autoinvoicing of that sales also been done ... then becuase of certain reason the sales order returned and hence i have created the negative line in the same sales order and give the corresponding reason of the returned and receiving the item from staging to concerned sub inventory as well  and also nullify its amount as zero using the credit memo .... now it is the business amount to un apply the return line ???

kindly suggest me the appropriate to do that thanx in advance

Regards,
Breath