How to resolve config from file and also few config programmatically?

Question

In my use case, I have a scenario where I want to populate some of the configs from the typesafe config file itself and some of those, I want to set programmatically. For example, for below myconfig.conf file

env=staging
topic=${env}_${event}

In above, snippet, topic should be resolved as staging_someevent event where someevent is set in one of the method which resolves this value based on argument in the job using args.

I am able to resolve one of those but not both. Below code resolves ${event}

String event = "someevent";
File file = new File("myconfig.conf");
InputStream inputStream = new FileInputStream(file);
InputStreamReader reader = new InputStreamReader(inputStream);
String configText = ConfigFactory.parseReader(reader)
  .resolveWith(ConfigFactory.parseString("event=" + event))
  .root
  .render(ConfigRenderOptions.concise().setJson(false));
System.out.println(configText);

Similarly, below code resolves ${env} but how can I resolve both?

String configText = ConfigFactory.parseReader(reader)
  .resolve()
  .root
  .render(ConfigRenderOptions.concise().setJson(false));
System.out.println(configText);