code: public function resetEnd($endColumn = null)
      {
          $endColumn = $endColumn ? $endColumn : $this->worksheet->getHighestColumn();
          $this->endColumnIndex = Coordinate::columnIndexFromString($endColumn);
  
          return $this;
      }
docs: (Re)Set the end column.
  
  @param string $endColumn The column address at which to stop iterating
  
  @return ColumnIterator