If you cannot execute it through the user interface, try editing the settings in the following file.
YOUR-WORKSPACE\.metadata\.plugins\org.eclipse.core.runtime\.settings
a file will appear called
org.eclipse.ui.browser.prefs , which will open it using any text editor and change the corresponding values. This self-description, you can easily find out what to change and that's it. Have a backup of the same before changing.
Hope this helps you.
EDIT: Restart your eclipse to complete the above change.
RP-
source share