You can start to merge your Fortnite accounts across all platforms: PC, Xbox, Switch, and PS4. It will take two weeks for all your in-game items and V-Bucks from other accounts to merge into the primary account. Start Here
Notice: You’ll need to access the emails that are connected to your different game consoles and the account must have been made before September 28th, 2018.
What items will merge?
Battle Royale players may merge all of their cosmetic items. Save the World players may merge their Llamas, Defenders, Heroes, Schematics, Survivors, XP, Evolution and Perk Materials.
Other Items such as Unreal Marketplace items, Creative Islands, and Save The World account level and progress will not be merged over from your secondary account. So if you’re worried that one account has less progress than the other, make sure your primary account is the highest.
Sources
The Gaming News Corner 