Managing self serve returns when customer uses own shipping

[Sjoberg]

We're looking at starting more automated returns on our store by using shopify self serve returns so all we need to do is accept or deny the request but we can't work out how to manage the returns when they arrive back to us if the customer uses their own shipping. Is there an option when you accept the return to send specific instructions to the customer telling them to put their order number in the parcel or are we missing something very obvious? Thanks!