How to make an iterative macro to loop over columns?

[Mond]

I don't have much experience with iterative macros - so would be great if you can link me some documentation/videos that might answer my question! I am trying to create a macro that will loop over data in a dynamic set of columns I get from an API and apply a formula to that data. Essentially I want to build a way to feed 1-3 or 1-5 columns into the iterative macro and have it calculate rolling sums for every column in the dynamic set.

I'm attaching a sample set for practice expected output given I only have field 1-3 available to start with. Hopefully someone can guide me in the correct path.