I’m trying to increase the number of a table’s columns in the the new reports 7.8, changing the column count does not change anything…what am I missing here?
Changing the column count probably is working, but you can’t see it because the width of existing columns doesn’t change. If you make the table larger or one of the visible columns narrower, you should see the new columns at the right.
I was changing the column count table properties but I needed to change column count in row properties.
now hunting data header option 
To change the details/headers column counts, you’ll want to ‘super-select’ the row you’d like to edit by clicking on the resize bar below it. So to edit the header of a new table, you’d enable the header by checking the box in the config panel, and then double-click the dark resize bar on the table below the header columns where it says “Object Header”.