Watch this tutorial on contacting participants in your tournament through email feature https://www.youtube.com/watch?v=7ZxA7xdcVEI
In your Manage screen, you'll find the Email Participants option in your navigation bar to the left. This allows you to send an email to every player in your tournament. Make sure your players receive the updates they need leading into or after your event.
If you are running a team based event, you can also email just the Pending Teams to give them updated joining information or a reminder that they need to get more players or finish registration.