Customize WooCommerce Cart Spinner

I'm looking for guidance to customize the spinner on the 'Buy Now' button in my WooCommerce cart page. Currently, the spinner simply loads without indicating the photo upload progress, which may confuse customers. I want to modify it to display the file upload percentage instead.

Key Requirements:
- Customize the spinner to show file upload progress.
- Provide detailed instructions for implementing changes.
- No direct site access available; theme files will be provided for editing.

Ideal Skills and Experience:
- Strong knowledge of WordPress and WooCommerce.
- Experience with customizing theme files and user interface elements.
- Ability to provide clear, step-by-step guidance for non-developers.
- Familiarity with JavaScript and AJAX for dynamic content updates.

I'm open to developing a plugin if necessary, but primarily seeking guidance to implement this customization myself. Your expertise in guiding me through this process would be greatly appreciated.