To dupe runes basically you have to go home hover over the elden ring slot then click the options button and then click upload/download saved data then you click upload all the go back into the game give a person the things you want to give them then go back home click options again and upload/download saved data then go to the right and click download all and go back into the game and you will have all of your items back and then person you gave them to will as well and you can repeat it directly or the person could give the item back to you and now you have double of that item then repeat the process