How to use sparkplug B

Hello, I’m trying to learn MQTT Sparkplug B, so I’m trying to test it out on my personal home project. But I also want to learn how it’s done in the industry. So, I want to control a PLC using sparkplug B, HiveMQ and Ignition Maker Edition.

Simplified case: I want to control temperature using the PLC. The PLC publishes the measured temperature every time the value is changed, that works okay. But I also want the setpoint to be published, but I also want it to be able to change it from Ignition and Node red. How is this done? As I understand, 2-way communication is not possible? How is this done in the industry?