To clear the assignment for an object just delete the object's folder.
Because the setting on the Admin user was being overridden by the object's parent container's setting you can delete the "Read parent containers of this object" checkbox from the fwViewAdmin.xml file for that user which will allow that user's settings to take priority. To do so open the fwViewAdmin.xml file in that object's directory and delete the following section:
Once that is done save, log out and back in and the Configure (or other) button should be there again.
A third option is to clear the View assignment on the parent container by changing the following section:
Change the section <![CDATA> to <![CDATA> (changing the 1 to a 0). Save, logout and back in and the icon should be back again.
In the fwViewAdmin.xml file should be a setting for each icon that is explicitly configured. Be sure if you mean to change the ConfigureView that you do not change the Favorites or some other view. For this reason the first solution, though the most "destructive" initially, is probably the most-sure solution to work.
These solutions do not require a restart of Tomcat but, if the user is logged in, they will need to log out and back in to see the change (Apache does not ever need to be restarted for an iManager change unless one of Apache's configuration files is changed such as httpd.conf).