You can find out whether you or the online shop bears the costs for the return shipment in the cancellation policy, which you can find either in your order confirmation or on the website of the online shop. If this information is missing, the online shop automatically bears the return shipping costs.
A list of certified shops with their contact details can be found here:
The cancellation policy also applies if the reason for the cancellation is, for example, damaged goods.
It is different if you have returned an incorrect or damaged product to the online shop under the statutory warranty and wish to exchange or replace it. In this case, the online shop has to bear the return shipping costs in case of a justified complaint.