Managing a custom challenge is done from the account that the challenge was created in. The additional management functions are available through the Invite, and Edit buttons that show below the challenge on the challenges page. These functions allow you to invite other people to participate in the challenge and edit the challenge.
Invites are sent by clicking the invite button, selecting a group (community) from the drop down menu and checking the names of the people you want to participate, and clicking the Invite button. This will send emails to the selected members registered email address inviting them to join your challenge. The email invite will include the instructions on how they can manually join the challenge.
The Edit Button
This button allows you to edit the details and settings for the challenge. This takes you to a screen just like the challenge creation screen where you can change every aspect of the challenge. Clicking the Update Challenge button at the bottom of the page will save any changes, while the Cancel button will discard changes.