It is possible to remove a card (or all related cards) at once. This action cannot be undone. When a card is created from an integration, it is not possible to remove a card. You can only archive these cards.
Open a planned card. Use the action button and select the option 'Remove card' or 'Remove related cards'. The card (and the collection) will be removed. Note: this action cannot be undone. Therefore you must always confirm this action first.