In a csv file you need a column named address or Address, with different addresses, you have to upload the file to the web app, and submit the file, you will get the latitude and longitude from every address in form of a new table, you can download the new table in a csv file.
jalfr3d/geocoder-app
A web app using flask to process addresses from a csv file and get latitude and longitude in a new file
PythonMIT