code: public function prev()
      {
          if ($this->currentColumnIndex <= $this->startColumnIndex) {
              throw new PhpSpreadsheetException('Column is already at the beginning of range (' . Coordinate::stringFromColumnIndex($this->endColumnIndex) . ' - ' . Coordinate::stringFromColumnIndex($this->endColumnIndex) . ')');
          }
          --$this->currentColumnIndex;
      }
docs: Set the iterator to its previous value.
  
  @throws PhpSpreadsheetException