To safeguard you from accidentally deleting some important data, before you delete a poll you need to make sure to clear any results first.
Follow these steps to clear & then delete a poll:
Select the poll you wish to delete.
Press the 'Clear Results' button on the right.
Press 'OK' on the confirmation message that appears at the bottom in orange.
To permanently delete the poll press the delete button .
Press 'OK' on the confirmation message that appears.