You can reverse the changes you made to your Performance Dashboard using Dashboard Builder.
When you are editing a dashboard, Dashboard Builder saves the previous version of the _def.xml and _properties.xml files of your dashboard in the backup subdirectory in Dashboard definition directory (e.g., <PPM installation directory>\ppmmashzone\server\bin\work\data_ppm\custom\<client>\webapp\performancedashboards) each time you save. The file names are given a version number, which increments each time. The files are named based on the pattern <Dashboard base name>_<version number>.
Example
umg_dashboard_7_properties.xml and umg_dashboard_7_def.xml
To restore a particular dashboard definition status, copy the configuration files of the relevant version to the top level directory, delete or archive the current _def.xml and _properties.xml files, and remove the version number section of the file name.
Example
umg_dashboard_7_dev.xml becomes umg_dashboard_dev.xml, and
umg_dashboard_7_properties.xml becomes umg_dashboard_properties.xml
Finally, you must relaunch the restored dashboard by selecting it from the dashboard list.