Changing prometheus image

I am installing Istio using the operator. I had issues fetching images from (throttling requests from corporate network) so I’ve pushed the images manually to an imagestream (running on Openshift) changed the ‘spec.hub’ in the CRD to my imagestream.

I didn’t found how to do that for the Prometheus instance as this is an add-on, not a component. Could you tell me where can I find the magic incantation in the documentation?