You need to set a uses-permission in a AndroidManifest.xml file
The permission will look like this:
<uses-permission android:name="android.permission.CLEAR_APP_USER_DATA"/>
And will be placed within the manifest element of the xml file.
You can set it using manifest designer in eclipse by opening the AndroidManifest.xml file, then clicking on the Permissions tab (at the bottom). Then click Add and select "Uses Permission". You will find the permission you are looking for in the list.
You will not be able to clear the user data from the app without this permission.
See more information on permissions here and here