Cannot save multiple checkbox value checked after a form submits on ajax load in php

I have one simple form which has: From date, To date When i click on submit i get list of car bookings on ajax load. In each row there is a checkbox to select that row and after multiple selection of row a common button is clicked to add bill on next page. Now my problem is I want to select multiple rows and again fill from date, to date and then submit form to get other list to again select other rows to add bill, now the problem is when I again submit form the old selected rows does not get saved so that i can get all rows selected all together on bill page. Right now below snippets are all working correctly but i have no idea how to do this when form is filled again and selection is done. Below code is only doing selection of current page. 1. This is ajax script

<script> $("#button").click(function(){
document.getElementById("loading").style.display = "block"; 
document.getElementById("overlay").style.opacity = '0.2';
var toDate = $("#datepicker2").val();
var fromDate = $("#datepicker").val();  
// var comp = $("#comp").val();
var dataString = 'fromDate='+ fromDate + '&toDate='+ toDate;
$.ajax({
  url: 'CloseBookingload.php',
  data:dataString,
  type: 'POST',
  success: function(result){
          // console.log(result);
           $("#load").show();
          $("#resultData").html(result);
           document.getElementById("loading").style.display = "none"; 
           document.getElementById("overlay").style.opacity = '1';
        }
      }); });</script>

This is my ajax page checkbox field after loads

 <input type="checkbox" id="checkselect" name="checkselect[]" value="<?php echo $row['car_booking_id'];?>">

This where checkbox values are fetched

    $checkselect=array();
if(!empty($_POST['checkselect']))
{
    $checkselect=$_POST['checkselect']; 
    $nc = count($checkselect);
    for($i=0;$i<$nc;$i++)
    {
    $dids = $checkselect[$i];
    }
    $ids = join(",",$checkselect);
    $booking_car = $db->prepare("SELECT * FROM `car_booking`
    left join driver_master on driver_master.driver_id = car_booking.driver_id
    left join vendor_master on vendor_master.vendor_id=car_booking.vendor_name
    left join company_master on company_master.company = car_booking.company
    inner join city_master on city_master.city_id=car_booking.action
    WHERE booked_status=1 and car_booking.slip=1 and car_booking.car_booking_id in ($ids)  order by  str_to_date( booking_date,'%d/%m/%Y') asc ");
    $booking_car->execute();
    $MyArr=$booking_car->fetchall();
    // print_r($MyArr);
    // die;
    $booking_car2 = $db->prepare("SELECT * FROM `car_booking`
    left join driver_master on driver_master.driver_id = car_booking.driver_id
    left join vendor_master on vendor_master.vendor_id=car_booking.vendor_name
    left join company_master on company_master.company = car_booking.company
    inner join city_master on city_master.city_id=car_booking.action WHERE booked_status=1 and car_booking.slip=1 and car_booking.car_booking_id in ($ids) order by  str_to_date( booking_date,'%d/%m/%Y') asc ");
    $booking_car2->execute();
    $r2=$booking_car2->fetch();
}

for($i=0;$i<count($MyArr);$i++){

    $NewIDArr[$i][0]=$MyArr[$i]['car_booking_id'];
}
$Mixed = $NewIDArr;
$r = json_encode($Mixed);
$RequestText = urlencode($r);
?>
    <input type="hidden" name="RequestText" value="<?php echo $RequestText; ?>"> 
    <input type = "submit" name = "update" value = "Update">

First Page IMAGE Main Page IMAGE

The page where actual values are fetched and updated

<?php
                require_once '../dbconfig.php';
                $r = urldecode($_REQUEST['RequestText']);
                $Mixed = json_decode($r);
                $bill=$_POST['bill'];
                $remark=$_POST['remark'];

                //$RequestText = $_POST['RequestText'];
                $singleArray = []; 
                foreach ($Mixed as $childArray) 
                { 
                    foreach ($childArray as $value) 
                    { 
                    $singleArray[] = $value; 
                    } 
                }


                // print_r($singleArray);
                // print_r( $bill);
                // print_r($remark);
                // die;7615, 7631

                    $nc = count($singleArray);
                    //print_r($nc);
                        for($i=0;$i<$nc;$i++)
                        {
                        $did = $singleArray[$i];
                        $data=array('bill_no'=>$bill,'remark'=>$remark);
                        $where = array('car_booking_id' =>$did);    
                        $update = $db->update('car_booking',$data,$where)- 
                       >affectedRows();

                        }
                        header("Location:close_booking.php");
                            //echo "Updated";

    ?>