It can be done from the "Leaderboard Preferences."
Here are the specific steps:
- Navigate to "Scoring"
- Select "Leaderboard" in the sub-menu
- Click "Leaderboard preferences" in the top right of the page
- Under the question "Would you like to divide your competition's leaderboard into divisions?" – Switch the answer to Yes
- Click "Update preferences"
- Add your desired divisions (under "Leaderboard divisions" at the bottom of the page)