Step one: Drive near the vertical support beam of any SC Jogos sign during an expert difficulty race
Step two: If you are using controller enter the secret code by pressing y-b-y-a-x-b (It works with keyboard, just use the equavilent mapped buttons).
Step three: Now a short cutscene should play during which your character model will step out of your F1 car, scale the sign, and begin to Fortnite default dance.
Step four: Enjoy!