A tournament can only be deleted if there are 0 registered participants (entries).
Only the organizer of the tournament can delete it.
Even if a tournament already has several registered participants, it can be deleted by deleting all participants. If you have already shared tournament information with participants, deleting it may seem abrupt, so please be sure to inform them.
You can delete a tournament from "Delete Tournament" on the far right of the "Settings" screen. Please note that deletion cannot be undone.