Editing a field

Hi, I imported a CSV file into my desktop for my fields, but I was wondering how I can go about adding new data into a cell on the chart. For instance if you see the month of June in YR2019, would I be able to add values into those cells, and if so how can I go about doing this?

I am trying to import data so I can create my visuals via R code.

https://imgur.com/3l5thrx