The intended audience for this article is Agents.
From the Forms index page (that lists all forms):
click the user's avatar
click "unassign x# questions" to unassign specific questions
click "unassign form" to unassign the entire form
From the Form itself
click the user's avatar
follow the same steps as above
To unassign a single question From the Form itself
look for the specific individual question you want to unassign
click the user's avatar
click "unassign"
Unassigning forms does not un-share the form (form visibility permissions). To turn off form visibility permissions:
head over to the "Collaborators" section on the left menu
click the collaborator you want to un-share forms with
click the pencil icon (edit)
remove view permissions by unchecking the "view" box
scroll down and click "save"