if you don´t have the game in the dashboard go to library

You cannot purchase skins while in other Fortnite modes.

Only a few skins are available in the Item Shop at any given time. The skins available in the Item Shop rotate every 24 hours.

If there are extra cosmetic items included with the skin, the button will read Purchase Items instead. If you don’t have enough V-Bucks in your Fortnite account, the button will read Get V-Bucks instead. Pressing the □ button in this situation sends you to the Store tile, where you can choose how many V-Bucks you wish to purchase. Once you’ve done so, return to the Item Shop and use the V-Bucks to purchase the selected skin. To view your purchased skins, press the O button, then select Locker from the menu at the top of the screen. Highlight the Outfit option in the Locker and press ✕. This shows you a page with all of the skins associated with your account. Select one and press +✕ to use it.