You can randomize challenge winners from the Challeges section of your Admin Portal by clicking the challenge leaderboard and then the ticket icon.
Step 1: Log into your Admin Portal at owner.myzone.org. Click Challenges.
Step 3: Access your challenge leaderboard
Step 4: Click on the ticket icon--this is the Challenge Randomizer.
Step 5: Set the MEP threshold and click the Draw field to enter the number of winners.