best way to defragment a table

We have a huge very active master database replicated to 16 other databases using goldengate. The application runs purges of many tables nightly and the application is insert and delete intensive. 3 of our biggest tables are partitioned. We are using oracle enterprise manager, db version 12.2.0.1. In the past we have done export/import but management won't allow that now. There is never a "quiet" time in the application and replication is always running. What is the best way to get rid of table fragmentation and free up some of the unused space?

Thanks in advance