To change the registration URL on the WordPress default login page, you can use a custom function in your theme’s functions.php file or a custom plugin.

1.Using functions.php
Access your theme’s functions.php file:
Go to your WordPress dashboard.
Navigate to Appearance > Theme Editor.
Select the functions.php file from the list of theme files on the right.

Add the following code:
Add the following code snippet to the functions.php file to modify the registration URL:

function custom_register_url($register_url) {
  //Replace 'https://your-custom-registration-url.com' with your desired registration URL
  return 'https://your-custom-registration-url.com';
}
add_filter('register_url', 'custom_register_url');

Save the changes:
Click the “Update File” button to save the changes.

2. Using a Custom Plugin
If you prefer not to modify your theme’s functions.php file, you can create a custom plugin:
Create a new PHP file:
Create a new file in the wp-content/plugins directory, e.g., custom-register-url.php

Add the plugin header and code:
Add the following code to the file:

<?php
/*
Plugin Name: Custom Register Url
Description: Changes the register url on the WordPress default login page.
Version: 1.0
Author: Your Name
*/

function custom_register_url($register_url) {
    //Replace 'https://your-custom-registration-url.com' with your desired registration URL
    return 'https://your-custom-registration-url.com';
}
add_filter('register_url', 'custom_register_url');

Activate the plugin:
Go to the WordPress dashboard.
Navigate to Plugins>Installed Plugins.
Find “Custom Register URL” in the list and click “Activate”.