Caution should be used with these commands as you can permanently erase data if you are not careful.
First check the list of snapshots that are present:
zfs list -t snapshot
To delete a specific snapshot:
zfs destroy -rv <snapshot name>
To delete all snapshots for a file system a wildcard can be used. As an example, if there is a ZFS file system named "myfs" in the storage pool "storage":
zfs destroy -rv storage/myfs@%