code: public function resetStart($startColumn = 'A')
      {
          $this->startColumnIndex = Coordinate::columnIndexFromString($startColumn);
          $this->adjustForExistingOnlyRange();
          $this->seek(Coordinate::stringFromColumnIndex($this->startColumnIndex));
  
          return $this;
      }
docs: (Re)Set the start column and the current column pointer.
  
  @param string $startColumn The column address at which to start iterating
  
  @throws PhpSpreadsheetException
  
  @return RowCellIterator