Issue Sales Order for your customer

When your customer returns the items, create Exchange and Return document to add the returned goods. (You can create Location named ''consignment" to place returned items)

Select Shipment (Delivery Order), add the Product(s), Location(s), Sections(s), Batch(es) (if have) and Quantity

After clicking Save, the item quantities will be returned back to your designated inventory location. You can check in Inventory List Report or Inventory Movement Report.