To edit an existing Report or add a new one, go to the Reports tab in the top navigation bar, and click on Customize. 
From the Reports drop-down menu, choose a Report you would like to edit. Even if you want to create a new Report, you would have to choose one of the Reports to serve as a base.
You can then change which information will be presented in the Rows & Columns of the Report, whether the Report show Interviews that were only conducted, or all Interviews that were scheduled, the date range and any Filters you would like to apply (Interviewers, Requisitions, Interview types, Assignees or Access levels).
After setting up your Report, you can click Run Report to present it, or Save Report to save it. To update an existing Report, save the Report using the same Report name, then choose the original Report and click on Remove.