Change the format of 1st column of the imported .csv from "general" to "date" in php

I had a .xlsx file with 2 columns (date, number). I converted it to a .csv file.
I have a mysql table with 2 columns (date, number).

I am trying to load this file into my table in mysql.

The first column (date) in my .csv file is in a general format but I want it to be in a date format like : %Y-%m-%d.

I am using the following code to convert the .xlsx to .csv and then import it in the database:

            $fileType=PHPExcel_IOFactory::identify($path.$file.'.xlsx');
            $objReader = PHPExcel_IOFactory::createReader("Excel2007");

            $objReader->setReadDataOnly(true);   
            $objPHPExcel = $objReader->load($path.$file.'.xlsx');

            $objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'CSV');
            $objWriter->save($path.$file.'.csv'); 

            // Load csv to table    
            $sql = 'LOAD DATA LOCAL INFILE \'path'.$file.'.csv\' INTO TABLE '.$dbtable.'
            FIELDS TERMINATED BY \',\' 
            ENCLOSED BY \'"\' 
            LINES TERMINATED BY \'\n\'
            IGNORE 8 LINES 
            (@date, number)
            set date=str_to_date(@date,\'%Y-%m-%d\')
            ';

            $Db->query($sql);
            echo $Db->error;

It works. My only problem is the format of the first column. I want to change it to a date format before loading the file into my table.