And how did they do it with travis scott and how did they do it with marshmello?
Epic Games / Fortnite of course program such events, there would be no other way, they have to "create" it. The Travis Scoot and Marshmello are cooperations.
Ok, did they actually request these 2 stars or how do they do it?
It's hard to say, it may have been that she asked Epic, but it could be the other way around