Establish accessibility of on web app in the GKE cluster from the internal network (VPN)

Question

I want to have an URL for my web app that is running in gke and that is only accessible from specific VPN. The web application should be accessible via HTTPS, i.e. valid certificates are configured accordingly

So for example I am in my corporate vpn and i have a conection between vpn and vpc. I Deploy want deploy this simple web app and want it to be accessible only trough my vpn.

    apiVersion: apps/v1
kind: Deployment
metadata:
  name: ilb-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: ilb-deployment
  template:
    metadata:
      labels:
        app: ilb-deployment
    spec:
      containers:
      - name: hello-app
        image: us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0

and I deploy a service of typ internal load balancer

apiVersion: v1
kind: Service
metadata:
  name: ilb-svc
  annotations:
    networking.gke.io/load-balancer-type: "Internal"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  selector:
    app: ilb-deployment
  ports:
  - name: tcp-port
    protocol: TCP
    port: 8080
    targetPort: 8080

I get an internal IP adress, but I cant open it from my vpn. What is the next step?