How to send ajax request from knockout js to controller php file

I am overriding shipping address in mixin js file , I want id in my controller when we move from checkout page next step.

/jshint browser:true jquery:true/
/global alert/
define([
‘jquery’,
‘mage/utils/wrapper’,
‘mage/storage’,
‘uiComponent’,
‘Magento_Checkout/js/model/quote’
], function ($, wrapper, storage,Component, quote) {
‘use strict’;

 return function (setShippingInformationAction) {

     return wrapper.wrap(setShippingInformationAction, function (originalAction) {
         var shippingAddress = quote.shippingAddress();
         console.log("Before");
        console.log(shippingAddress);
                 var countryId = quote.shippingAddress().countryId;
            
             if (shippingAddress['extension_attributes'] === undefined) {
            shippingAddress['extension_attributes'] = {};
        }
        
        var attribute1 = shippingAddress.customAttributes.find(
            function (element) {
                return element.attribute_code === 'eventid';
            }
        );
        var attribute = shippingAddress.customAttributes.find(
            function (element) {
                return element.attribute_code === 'custom_field';
            }
        );
        shippingAddress['extension_attributes']['custom_field'] = attribute.value;

        shippingAddress['extension_attributes']['eventid'] = attribute1.value;
          
        
         
         // ajax call
         

        var param = 'ajax=1';
            $.ajax({
                showLoader: true,
                url: 'http://127.0.0.1/magento237new/test2.php',
                data: {eventid: attribute1.value},
                type: "POST",
                dataType: 'json'
            }).done(function (data) {
                console.log(data);
            });
    
                                         
         console.log("After");
        console.log(shippingAddress);
         return originalAction(); // 
     });
 };

});