As Karthiga_R suggested, the LED implementation can be referenced from LedsAndButtons in workbench.
For MQTT topic subscription, you can define your custom topic in MqttSubscribeInfo in SendDataOverMQTT example application.
To implement you custom application, you can modify the functionality in AppMQTTSubscribeCB function.
The example applications are simple enablers, upon which developers can start their custom applications.
Hope you can modify your application based on the references in the example applicaitons.