...
By default any new reports created will be a single report. If you wish to build a multi report click convert to multi report from the top of the page. It is not possible to convert from a multi report back to a single report.
Multi reports can be embedded within events and dashboard tiles in the same way as single reports.
...
This will change the edit interface to one which allows you to define many reports within the same template. The configuration already defined within the single report from which you converted will be carried across and added as a new report element.
...