Depending on the campaign type, you may have multiple choices.
For recently updated experiences such as Polls, Sweepstakes, and UGC contests, go to the Participants tab and click Pick Winners.
On the popup, select the number of winners to be chosen (if more than one) select a date-range (if applicable) and click Pick Winner.
Top Votes – In a Photo, Video, or UGC contest, you can also choose winners based on highest vote counts. To see these entries, visit the Submissions tab and click Top Voted.
For older campaign types, just go to the Winners section under the Manage tab and click Pick Winners.
This lets you pick winners at random, choose one at a time, or multiple at once. You can also choose between specific dates of entry as well.
Referrals – Only available in Brackets, Pin-To-Wins, and Quizzes, this will show you the top 50 users with the most referrals. If you want to award users based on referring others into the contest, you’d want to look here to see who referred the most people.
Your campaign will not automatically contact winners when they’re chosen. You can send them a personalized email or contact them through other means (Facebook promotional guidelines do require you to contact them outside of Facebook, however).
Posts – You can also pick winners from reactions or comments from Facebook, Instagram, or YouTube posts. You can find more info on picking winners from posts here.