如何减少AWS RDS中的Oracle撤销表空间?

Undo tablespace in my Oracle DB is taking 180GB. I don't have any process that would need this much space. There was an unknown issue with the DB, which cussed the undo table size to increase back in a while; and after bouncing RDS instance it has been rectified. The issue now is how decrease the size of the undo tablespace. I have managed to create a new undo table using Undo tablespace in my Oracle DB is taking 180GB