How do I clone a website that is hosted on Google App Engine?

How do I clone a website that is hosted on Google App Engine?

I have a friend's website hosted on Google App Engine and he wants a some
changes to be done. He wants to download the assets from there and build
it from scratch into a different host provider. Thing is, when I enter in
the Google App Engine Dashboard I find it so hard to export/download
anything. All looks so messy. I can't even find the index.html and css
files. Any answers would be really appreciated. Thanks.