Once you uploaded the WP-Stateless plugin, you will be redirected to Set up Assistant which will navigate you through all the 3 steps
Login with the Google Account you want to be associated with your website and consent to the permissions request.
Set up Google Cloud Project and Bucket names. By default we are creating new project and bucket for you
That's all. Try to upload something. Any media file you upload to WordPress will now be uploaded to Google Cloud Storage and served to your users from Google servers!
Now all image's links will go to Google Cloud Storage. You could also edit and regenerate single image.
You can also regenerate all your existing images