Open your report and select the date range option (calendar icon) in the navigation bar. Under "Primary dates" choose a date range you want to view data for. Few shortcut options like last month, this week, etc. help make quick changes.
Now under "Compare with", choose the date range to set the reference you wish to compare your primary data with.
Click on apply to save these changes throughout your platform.
Additionally, clarisights provides you the option to override dates for widgets causing the changes to happen only to it. Learn how.