Hello, Naveen. This error message means that in your current AML workspace, there already exists a real-time endpoint(or service) whose name is "diabetes-service", so you can't deploy a new service with this same name because it will cause duplication.
You can check your workspace in our portal https://ml.azure.com/selectWorkspace , in the sidebar you can find a "Endpoints" button, you can find all your "real-time endpoint" there. Then please delete the dup service, after deletion you can deploy your new service with the name "diabetes-service".