This article elaborates how to return items to the vendor/supplier. To do so, first create a contact as vendor and save it.
Then from the inventory section, select new stock movement under the stock control tab:
On the following window, select, the document type as "Vendor Return", then "Location" and the Vendor.
Add the items to the pricing table and Email this document to the vendor:
After marking it as done, the status is changed to "in progress":
Once you have the items in hand, click on send items button and adjust the amount of items being sent to the vendor:
Then, the status is changed to completed.