How do I declare default MQTT Topic in this SDK?

[HKPhysicist]

Dear Developers,
I am subscribing a Maker Plan of Thingsboard Pro.

I follow this example and programmed it on my Adafruit ESP32 S2 board. After having corrected issues referred by other developers, I get it running and connected to my Thingsboard panel through MQTT and MQTTS. At this stage, there is no issue.
https://github.com/thingsboard/thingsboard-client-sdk/tree/master/examples/0003-esp8266_esp32_send_data

However, the telemetry data does not show up inside my Thingsboard panel of my newly created device. It only shows "Active". I guess the cause is that there is no way to declare MQTT Topic from within your example codes shown in the above link.

I do not need custom topics. It is just the default topic created by Thingsboard Pro panel for my device:
-t esp/telemetry

So, what is the standard way to declare a MQTT topic in your thingsboard-client-sdk? Please advice.

Yours faithfully,
Timmy