If you've built a great report and you want to make a copy so you can tweak it or change filters, you can simply copy and paste the report into a new location.

You need to locate the report you would like to copy within the side bar.
To do this, open the side bar and locate the dashboard you are currently on : it will be highlighted in blue:

You should then click the arrow to the left of the dashboard name : this will expand the tree to show all reports on this dashboard. Click the three dots to the far right of the report that you want to copy and click 'Copy':

You can then paste this report into any other dashboard to which you have edit access. 

Click the three dots to the right of the dashboard you want to copy into and click 'Paste':

Please note that you can only paste into dashboards - not into folders - and you must have Edit access to a dashboard in order to paste new reports into it.