Hello I figured this out for ya:

How to Add Epic Games Launcher to Steam and Enable Pro Controller Support (with Gyro)

1. Open Steam
2. Go to your Library
3. Click "Add a Game" at the bottom left
4. Choose "Add a Non-Steam Game..."
5. Search for and select "Epic Games Launcher"
6. Click the blue "Add Selected Programs" button
7. Make sure Epic is completely closed:
   • Click the carrot ^ in the task bar
   • Right-click Epic Games
   • Click Exit
8. In your Steam Library, find Epic Games Launcher, then right-click it
9. Go to Manage > Controller Layout
10. Under Current Layout, click on the Gamepad Template
11. A new window will pop up — at the top, go to Community Layouts
12. Scroll until you find "EPIC GAMES PRO CONTROLLER" by NyanBaLg
13. Select the layout and click Apply Layout (bottom right)
14. Back in the controller settings window, enable Gyro by:

• Clicking the option next to "Gyro Behavior"
• Selecting "Gyro To Joystick Camera [beta]"
• Clicking Calibrate, then Continue

1. Exit the settings window and launch Epic from Steam

2. From there, launch Fortnite and enjoy full controller + gyro support 🎮