How to change company logo in nbdev

I would like to change the icon that shows at the bottom right of every page (it currently shows the fastai logo, which is the default).

I have tried replacing the png under docs/_site/assets/images and then did nbdev_build_lib, nbdev_build_docs, … git push. It (obviously?) didn’t work (since the _site folder is ignored). Any idea how I may get this done?
If it is not meant to be changed, I don’t mind keeping it in there but would like to know anyway.