foreach($data as $k=>$v){
    // print_r($v);

    foreach($v as $key => &$val){

    if(preg_match("/^(((0[13578]|1[02])\/(0[1-9]|[12]\d|3[01])\/((19|[2-9]\d)\d{2}))|((0[13456789]|1[012])\/(0[1-9]|[12]\d|30)\/((19|[2-9]\d)\d{2}))|(02\/(0[1-9]|1\d|2[0-8])\/((19|[2-9]\d)\d{2}))|(02\/29\/((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/",$val)) {

    echo "match!";

    $originalDate = $val;
    $newDate = date("Y-m-d", strtotime($originalDate));
    $val = $newDate;
}

}
}