How do I add columns to a report?

Go to "Reports" and then "All reports" in the left menu. Click on the "Drafts" tab. Then click on the icon with three dots and select "Edit" on the report you want to edit. 

In the menu bar, select the icon called "Add columns". You can choose to add multiple columns to a report. If you want to save your report click "Save" or if you want to preview your report "Save and show".