convert Hex result of sensor to integer value

Projects Programming
5 
SoftwareSerial mySerial(10, 11); // RX, TX

So, you have a mySerial connected to these pins. Post a picture of the mySerial that is connected, so we know what a mySerial looks like.

  // Send message to sensor, which make it send back data.  byte message[] = { 0x55, 0xAA, 0x7E, 0x02, 0x4F, 0x43, 0x94, 0x0E, 0x0D };
  Serial.write(message, sizeof(message));

Why isn't the sensor connected to the software serial instance, so you can use Serial to debug your code?

    int readout = Serial.read();
   
    /*** Code to interpret HEX answer of the sensor.  ***/
   
  }

You are not storing the data, or even printing it, so you have no proof that the sensor returns the data you think it does.