Your canonical Fortnite information lives in your Epic Games account. Link that account everywhere you play, and your progress and purchased content travels with you. (Stats and leaderboards are platform-specific, though.)
So, if you want to play with friends across platforms, everyone needs to link their platform’s account — iOS, PlayStation Network, Xbox Live or Nintendo Network — to their Epic Games account. If you already have an Epic Games account, you can link Fortnite to your PlayStation and Xbox accounts on the game’s official site. (Click on the the icon that looks like a person on the right side of the top menu.) On the Nintendo Switch, you’ll be asked to login when you start the game.
download this on pc:
https://www.epicgames.com/fortnite/en-US/download
Then login here and link your Xbox Live account to your epic account
https://www.epicgames.com/fortnite/en-US/buy-now/battle-royale
Once you do that I'll be able to find you.