From this short description, you can learn how to delete a worksheet permanently.
To permanently delete a worksheet, click at the bottom of the worksheet card, and then click the Settings menu or select the Move to bin button from the list.
It is important to note that the worksheets do not take up any storage space on their own; only the submissions, tasks, and uploaded attachments do. If you delete the worksheet, these will remain retained, which you can delete separately in the Repository to free up storage space.