Ok i found how to do it thank you!
include 'Classes/PHPExcel/IOFactory.php';
$objReader = PHPExcel_IOFactory::createReader('Excel2007');
//we load the file that we want to read
$objPHPExcel = $objReader->load("test.xlsx");
//we change the file
$objPHPExcel->getActiveSheet()
->setCellValue('A1','EEEEEEEEE')
->setCellValue('A2','DDDDDDDDDDDD')
->setCellValue('A3','CCCCCCCCC')
->setCellValue('A4','BBBBBBBBBB')
->setCellValue('A5','AAAAAAAAAAAAA')
->setCellValue('A29','MaitrePylos');
//we create a new file
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
//we save
$objWriter->save('coco.xlsx');