Groupies
The Groupies section in a goal's settings allows you to turn a goal into a group goal by adding people to join it. To add someone, you'll need to put in their username here, click "Add groupie", and wait for them to confirm being added to the goal.
Currently, if someone wishes to be removed from a group goal, you'd need to contact the support team. Either the original owner of the goal or the person who has been added to it can contact us about this and ask for changes.