If you have accidentally entered a distance multiple times or have entered an incorrect distance then you will need to delete that distance, which is super easy when you know how!
In The Conqueror App:
Go into the Challenge. Tap on the right hand menu and choose the "Newfeed" icon (2nd from the bottom), change the Filter to "Just me" and you'll see all your distances. To delete tap the cross above the distance you wish to remove and then confirm that you wish to delete it.
Tab the Bottom Left "Progress" icon and then at the top tap the right hand tab "View Distances". This will include distances for all challenges and if they were posted to multiple challenges they will appear multiple times. To delete tap the cross above the distance you wish to remove and then confirm that you wish to delete it.
Hope this helps.