It could be that a return request was submitted not via a special Return button in a customer account but through some other sources of communication (regular email, phone call, etc.), and hence was not recorded on the “Returns” page of your store Admin area. It could also be that a store admin needs to issue a return for an order for some other reason.
If this is the case, you have an opportunity to create a return for an order using the Create return tab of the order details page:
To document the return on behalf of a customer:
Locate an order you need to return on the order listing page (Orders -> Orders list) and open the order details page.
Open the Create return tab of the order details page;
Choose items, specify the reason and add comments if required;
Click Submit return.
The claim for return will be submitted, transforming the page into a regular Order return page where a store admin can either authorize or decline the claim for return, as described in Processing Customer Requests for Return.