How can i play fortnite with a second account on the pc?

I log out with my main acc and log in with a new acc but can't start fn because it says I have to get the game first but I can't get it at all

Why not?

Yes, I have no idea I'm logged in with the new account but can't start fn because it says I don't have the game although I can't download it

No I mean why don't you get it?