Data loader

[Ami]

Hello
Lets say i have a working app that users work with.
However, lets say that currently my users already have data in excel. Instead of manualy adding all the data, i want them to be able to load existing data via csv and have the app preform all it’s functionality on set uploaded data, for instance, assign uniqueid.
I want this to be acheived by my users rather than by me as the developer. How can something like that be done?