How to use Data Flows to incrementally add to a data set for pro users

I understand that the incremental addition to data sets is a feature only available to premium users.

I am a pro user.

From my research I believe the use of data flows enables pro users to incrementally add to data sets.

example

I have a .csv file that I download from an app and the data download limit is one week.

I want to download the data weekly and build a data set over time building up a historical data set.

So i will have data set A historical data stored in a table in PowerBI

And i will add to this by the weekly upload of .csv data for the current week

append data does not solve this issue in this context.

I cannot find a simple explanation of how to do something like this on youtube or via guy in a cube etc.

A simple demo of how to use data flows with .csv files would be brilliant.

Does any one have a solution for this?