The best way to have customers return product directly to the manufacturer is to set up a return policy with the manufacturer and make it clear to customers on the product packaging and website. You can also include a return shipping label with the product package and provide customers with instructions on how to return the product to the manufacturer. Additionally, you can make sure that your customer service team is available to answer any questions customers may have about returning the product.
You can set up a returns portal that allows your customers to generate returns labels on demand, saving you the time and effort to produce returns labels yourself. The address on the return label can be the manufactures address and once the package has arrived there you can get an alert to refund the customer. Check out ibundle.