Independetly of Oracle WebCenter Portal or Content the RCU utility has been included as part of the Oracle Fusion Middleware Infrastructure that you need to install as pre-requisite in your WebLogic Domain.
I strongly suggest you read the https://docs.oracle.com/en/middleware/lifecycle/18.104.22.168/inecm/product-installation.html#GUID-4A150924-9210-4788-8DE1-54… to understand the installation process of WebCenter Content.
If you are installing WebCenter Content in the same domain as Portal you already probably have RCU as you installed the Infrastructure installer (ADF,MDS,JRF...).
The Fusion Middleware Infrastructure you can installed it bundled with WebLogic or just download it separately and apply it over a WebLogic Domain.
You can find it in the WebLogic Downloads as Fusion Middleware Infrastructure Installer: