Knockout.js - Form reset

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<div id="bookform">
   <input type="checkbox" id="checkbox1"  data-bind="checked: checkBox1, click: checkboxStateChange"> Checkbox 1
   <input type="checkbox" id="checkbox2"  data-bind="checked: checkBox2, click: checkboxStateChange">Checkbox 2
   <button type="button" id="myBtn" class="btn btn-primary submit-btn" data-bind="click: onButtonClick">Submit</button>
</div>

CSS

h3 {
  font-size: 120%;
  font-weight: bold;  
  margin-top: 5px;
}
#bookform {
  margin: 10px;
  padding: 20px 20px 25px 20px;  
  background-color: #eee;
}

input {
  width: 100%; 
  padding: 4px;
}
.button {
    margin: 12px 0 0 0;
}

JavaScript

$('.submit-btn').attr('disabled', true);
var checkbox1 = document.getElementById('checkbox1');
var checkbox2 = document.getElementById('checkbox2');

var ViewModel = function() {
    var checkboxesChecked = false;
    self.checkBox1 = ko.observable(false);
    self.checkBox2 = ko.observable(false);
    self.checkboxStateChange = function() {

        if ((self.checkBox1() === true && self.checkBox2() === true) || ($("#checkbox2").length <= 0 && self.checkBox1() === true) || ($("#checkbox1").length <= 0 && self.checkBox2() === true)) {
            $('.submit-btn').attr('disabled', false);

        } else {
            $('.submit-btn').attr('disabled', true);

        }

        return true;
    }

};

ko.applyBindings(new ViewModel()); //