My little cousin played fortnite on my s10 once.
He told me that he got the IKONIK skin.
So when I tried to redeem it myself, I could not get it anymore, because he already did
Can someone help me with this problem?
You will need to contact Epic for assistance. https://www.epicgames.com/site/en-US/customer-service
That is because the promotion is one skin per device. Since your little cousin already redeemed it on your S10 you can't redeem it on the same device for another account