Yes leave can be cancelled. But staff cannot cancel it from ShiftCare App once its approved. They can only delete the leave if its status is pending i.e unapproved. It need to be cancelled by employer from their end after it is approved.
On clicking on approved leave, following page will open. Press "Decline" tab.
On pressing Decline tab following page will open. User will need to give reason of cancelling/declining shift and the press "Decline" button.