How do I run a startup script to create a Milvus DB on a GKE private cluster via Terraform?

Question

I am trying to create a Milvus DB on a private GKE cluster. I have created the cluster using Terraform. I now want to run a .sh script that will create a Milvus DB on the cluster that follows this script (https://milvus.io/docs/gcp.md). However, I can't run the script because the cluster is private.

I have tried:

1. Using local-exec and remote-exec provisioner
2. Bastion Host

But, none of these work.