You can remove an answer for the permissions by navigating to the students' tab on the left-hand menu, searching for the student, and from the Actions menu next to that student, clicking on Edit.
Now you will have tabs at the top. Select Permissions and you will see all permissions for that student:
If you click on the Remove button next to the permission the parent wants to change, that permission will show as 'Awaiting Response'. The permission can then be resent to the parent/guardian.