Welcome
Please first read this Some basics on Android storage system
So you have a csv file and would like to modify it from within the app, but also from outside the app...
After it has been modified outside of the app, you will need SAF to be able to read it again...
You can work directly from the shared storage /Documents, no need to hsd ASD I your case...
Alternatively you might want to think about a Google Spreadsheet solution... like this you can avoid sll the challenges with the file system
Taifun