Unfortunately, RiaB does not support deploying Helm chart onto the existing K8s clusters.
As you can see the doc, basically RiaB is to create a SD-RAN test environment from installing K8s to deploying Helm charts.
It should be running on the clean Ubuntu 18.04/20.04.
Otherwise, it should not work.
If you do want to deploy OAI nFAPI emulator, I recommend you to deploy RiaB on the Ubuntu first and then see how it works.
Once you understand all about the network connectivity and configurations, you can manually deploy OAI nFAPI emulator on the existing cluster and configure network parameters.