Navigate to one of the rosters on the left hand side: Enquiries, Applicants, Students, Families, or Alumni.
Click the three dot icon near the top right of the roster.
On the dropdown menu, tick the checkbox next to the columns you want to add. If needed, you can drag the individual column upward or downward to change the order of the columns on the roster. Then click Save when you are done.
As a note, if you add columns to any one of the Enquiries, Applicants, Students, or Alumni rosters, the other three rosters will be updated as well. You will need to do this separately with the Families roster.