You can edit your mission from the mobile app or on the website.
Note that only a mission admin can edit a group mission
Log in at www.myvirtualmission.com
Go to your mission page (if not already there)
Click "Mission control" at the top and then "edit mission"
Edit your mission on the map and update the origin and destination fields.
Tap top left menu icon
Select "Me and my missions"
To the right of the screen there is a little pencil icon - tap it
Edit the map and/or tap "next" top right
Change any details your want
Hope this helps!