I want to purge a change table for those data for which the subscriber has not been able to call PURGE_WINDOW. Now is it possible ? tehn how?

I know that a change table can be forcefully dropped while active subscribers still exist
by using the force option of DBMS_CDC_PUBLISH.DROP_CHANGE_TABLE

Now Can I purge forcefully those data for which subscriber do not call purge_window ?
otherwsie the size of the change table gets growing since not calling of purge_window.

Using which script can I install JVM and how to check whether that is installed or not?