Let's say you have a NFT, a cryptokitty, and you want to use it as your avatar in Fortnite. How would someone else be able to use it as their avatar if Fortnite

Let's say you have a NFT, a cryptokitty, and you want to use it as your avatar in Fortnite. How would someone else be able to use it as their avatar if Fortnite requires you need to prove that you own it?