code: public function prev()
      {
          if ($this->currentRow <= $this->startRow) {
              throw new PhpSpreadsheetException("Row is already at the beginning of range ({$this->startRow} - {$this->endRow})");
          }
  
          do {
              --$this->currentRow;
          } while (($this->onlyExistingCells) &&
              (!$this->worksheet->cellExistsByColumnAndRow($this->columnIndex, $this->currentRow)) &&
              ($this->currentRow >= $this->startRow));
      }
docs: Set the iterator to its previous value.