Hello,
I published an app with Streamlit Cloud. In this application, the user can enter data and the data he enters is stored in an excel file. So there is an excel file that is constantly updated according to the data entry. Let’s say 10 days later, I wanted to download the excel file with all the new data entered. Where can I find and download this excel file?
Where you have saved it 
https://docs.streamlit.io/library/api-reference/widgets/st.download_button
Apart from that, you have to take care of the handling of the users and the saved files yourself.
However, this is too little information to be able to say more about it. If you need more tips, please share the link to your public github repo.
Thank you for download suggestion. I need to know basically if I can access the data storage area. Your answer is not explained my question.
For example, when we publish a site on the web, we can access all its files. I want to know if such a situation is possible. My questions may be very basic but I’m trying to understand the logic and the way it works.
You can host a few basic types of static files on your app and access them from a url How to host static files in Streamlit? - Streamlit Docs. You might have trouble with an excel file, because it will be served as a plain text file, but a csv should work fine.