How to pass headers with namespace through SOAP UI?

I am working through a legacy project .

 {
  using(var scope = new OperationContextScope(client.InnerChannel)) {
    var appKeyMsgHeader = new MessageHeader < string > ("app1"); //Input parameter passed to the current method
    var appKeyUnTypedHeader = appKeyMsgHeader.GetUntypedHeader("AppKey", "Au.CustomHeaders");
    OperationContext.Current.OutgoingMessageHeaders.Add(appKeyUnTypedHeader);
    client.InnerChannel.OperationTimeout =
      TimeSpan.Parse(ConfigurationManager.AppSettings[BatchConstants.DisPatcherClientOperationTimeout]);
    output = client.Process(input);
  }
}, appKey);

This is the code for consuming the WebService. But I don't know how to consume the same from SOAP UI. Adding the simple header is not working. There is some tricky part with namespace and header. How to pass this through SOAP UI?