In WordPress it little bit complicated then default way to handle ajax. Modify your js code like this.

    function ajaxSubmit(e){
        
        // prevent the default action.
        e.preventDefault();
    
        var myform= jQuery(this).serialize();
    
        jQuery.ajax({
            type:"POST",
            // Get the admin ajax url which we have passed through wp_localize_script().
            url: ajax_object.ajax_url,
            action: "submitAjaxForm",
            data: myform,
            success:function(data){
                jQuery(".records").html(data);
            }
        });
    return false;
    }

In above JS code I have replaced the form url and added action parameter. Wordpress gives us a unified file to use that is admin-ajax.php.  It is used to call the server side PHP function through admin-ajax.php. If an action is not specified, admin-ajax.php will exit, and return 0 in the process. 


**Why form url replaced with ajax_object.ajax_url ?** 

This is because it is used to call the server side PHP function through admin-ajax.php. If an action is not specified, admin-ajax.php will exit, and return 0 in the process.



**Define form action.**

To define the form action, we need to add these action using `wp_ajax_` and `wp_ajax_nopriv_` as prefix. With callback function to handle those form data.  
Example. 

    add_action('wp_ajax_{YourFormAction}','{CallbackFunction}');`
    add_action('wp_ajax_nopriv_{YourFormAction}','{CallbackFunction}');

Add this code to `functions.php` file

    add_action('init', 'registerFormAction');
        
        function registerFormAction(){
        
            // To handle the form data we will have to register ajax action. 
            add_action('wp_ajax_nopriv_submitAjaxForm','submitAjaxForm_callback');
            add_action('wp_ajax_submitAjaxForm','submitAjaxForm_callback');
        
        }

**Handle ajax form data** 

Put your all code which is going to handle the form data, Inside the callback function which we have recently hooked with the `wp_ajax_{yourAction}` above.  

    function submitAjaxForm_callback(){
    
        if (isset($_POST['store_list']) && $_POST['store_list'] != 'Select by Store'){
                $store_list = $_POST['store_list'];
                $stores= $wpdb->get_results($wpdb->prepare("SELECT malls FROM tablename WHERE stores= '" . $store_list . "' AND code IN ('test3') ORDER BY street ASC", OBJECT));
                foreach ($stores as $record_s){
                    echo '<div class="records">';
                    echo '<div><span>' . $record_s->malls . '</span></div>';
                    echo '</div>';
                }
            } elseif (isset($_POST['street_list']) && $_POST['street_list'] != 'Select by'){
            $street_list = $_POST['street_list'];
            $streets = $wpdb->get_results($wpdb->prepare("SELECT street FROM tablename WHERE street_list= '" . $street_list. "' AND code IN ('test3') ORDER BY stores ASC", OBJECT));
            foreach ($streets as $record_m){
                echo '<div class="records">';
                echo '<div><span>' . $record_m->stores . '</span></div>';
                echo '</div>';
            }
        }
        
        // It is necessary to terminate the get proper data.
        wp_die();
    }