Once you create a challenge you can edit the name, description, photo and other settings until other people join. Here is how:
Go to For You > Challenges
Tap on the challenge you wish to edit
Tap on “…” in the top right
Select Edit from the menu
Make changes & select Finish
You can also delete the challenge by selecting Delete from the “…” menu.
NOTE: If you receive a message that you’re no longer able to Edit or Delete, it means other people have already joined and stared your challenge.