I have several purchases from the same person in auctions. How can I combine their shipping costs into 1 parcel?

@aimelesrobots , Lisez ceci : https://www.ebay.fr/help/selling/shipping-items/shipping-rates/offering-combined-shipping?id=4169&st=3&pos=1&query=Proposer%20la%20livraison%20group%C3%A9e&intent=port%20group%22&lucenceai=lucenceai&docId=HELP1130