Update all rows loop to create an updated column


I’m trying to create a feature that with one click will update a whole column in my local data source.
this thing I don’t believe is possible so the realistic option is to update every cell alone in the column.
my question is how can I create this kind of a loop?
this data source is dynamic and new rows are supposed to be added from time to time so there is no static number of rows.

thank you!