Istio service connection

My frontend service is calling to a backend service and fetching the data. If I replace one of my existing microservice(say frontend) with a new one(new frintend service), then do I need to change the gateway configuration for the same ? or istio will take care of the service connection between the frontend and backend. I want to know the working principle of istio in case of any code changes to the existing application or addition of microservices to the existing application.