Once your peer-to-peer event has been created, you can go back and edit content and settings at any point. You will find all of your active events from the Events & Campaigns tab. The dropdown menu at the top will allow you to search by "active" events or "past" events. Click on the event you wish to edit.
You will then be able to update any content, text, images or event settings. Hit "publish" and your changes will go live on your event.