laravelにspreadsheetをインストール
/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader

Html.php
を開いて
if (isset($attributeArray['rowspan'], $attributeArray['colspan'])) {
}
の最後に以下を追加する

$sheet->getStyle($range)->getBorders()->getTop()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);
							$sheet->getStyle($range)->getBorders()->getBottom()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);
							$sheet->getStyle($range)->getBorders()->getRight()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);

$sheet->getStyle($range)->getBorders()->getLeft()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);

以下のようにする



if (isset($attributeArray['rowspan'], $attributeArray['colspan'])) {

                            //create merging rowspan and colspan
                            $columnTo = $column;
                            for ($i = 0; $i < $attributeArray['colspan'] - 1; ++$i) {
                                ++$columnTo;
                            }
                            $range = $column . $row . ':' . $columnTo . ($row + $attributeArray['rowspan'] - 1);
                            foreach (Coordinate::extractAllCellReferencesInRange($range) as $value) {
                                $this->rowspan[$value] = true;
                            }
                            $sheet->mergeCells($range);
                            $column = $columnTo;
							$sheet->getStyle($range)->getBorders()->getTop()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);
							$sheet->getStyle($range)->getBorders()->getBottom()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);
							$sheet->getStyle($range)->getBorders()->getRight()->setBorderStyle(\PhpOffice\PhpSpreadsheet\Style\Border::BORDER_THIN);
							
                        }