To unassign a formative from your class or guest students*:
Go to "Assign"
Select the class it's actively assigned to
Click "Adjust Settings" or the pencil icon
Click on the trashcan icon next to the "View Responses" button:
Unassigning a formative from students in a class will cause their responses to disappear from your View Responses page and Tracker.
However, you can re-assign to the same class and their data will re-populate.
*Please note: unassigning a formative from guest students will cause their data to disappear from your View Responses and since those accounts are temporary and students can't log back in, you cannot re-assign to them.
If you want to hide formatives from your students while keeping data in your account, you can do this in your After Submission settings.