I know it is a very simple question, so probably not necessary to have a blog post about it, but I hope it helps you in case you do not know where Azure Machine Learning store the Notebooks.
To find your notebooks go to your Azure Machine Learning Storage Account -> File Shares
As you see in the image below you will find a folder called code-*
Find your Notebook folders
Inside your folder you will find your Notebooks.
I hope you find your Azure Machine Learning Notebooks.
My recommendation is to use git to commit/push the code to a repo.