Data Labeler - Save data and develop

Hi. I am trying to develop a Data Labeler app. The idea is simple: I mount the disk, load a .csv/s (or .json/s) into the data folder related to the app, and then I load the file/s in my app.
This file/s have only 2 columns or variables: "Messages", that contain texts, and "Labels" that are empty. In the app I may choose a file, read it, and message by message have the label options (0 or 1... Yes or No...) which are stored in the column "Labels" and saved in the file. Once the message is labeled, the app jumps to the next message until the column "Labels" is filled.
The idea behind this is to ease the tedious task in Data Science of labeling data, I think I will enjoy it much more just by cranking it out and then loading the files labeled back to my pc.

The problem: I suspect that saveGameData() is the solution to this, but I did not manage to replicate the playdate structure (games, data... folders) when developing in the sdk and the emulator, so it does not load or save anything in my tests. Besides, I didn't find a way to apply this methodology to .csvs (I mentioned that .jsons may work too).

How to structure my developing environment so I ensure load and save works in the emulator and in the Playdate as well? How to load and keep saving the files?

PD: I tried to simplify the problem by reading .txt and saving them with something additional, but didn't find the way either. Perhaps with this simple step I may get the concept behind this.