It is recommended to set a static IP to be used by the LoadBalancer service deployed by istio. To do that set spec.components.ingressGateways[0].k8s.overlays[0].patches[0].value, which is commented out by default, which causes the use of an ephemeral IP.
Create the istio-system-namespace:
kubectl apply -f ./istio/istio-system-namespace.yaml
Verify that your istioctl version (istioctl version) matches the version in istio/gerrit.profile.yaml under spec.tag.
Install istio:
istioctl install -f istio/gerrit.profile.yaml