Industrial PH-Sensor (S-pH-01A)

i just got this industrial grade ph sensor:

It should be calibratet by factory but i measured some liquids and it seems like it needs a new calibration or it hasnt been calibrated correctly.
I got another sensor with the same probe but another transmitter and other sensors to compare.

Is there another way to calibrate it than with Modbus RS485?
And if not, which software can i use for RS485 communcation?
I use an esp32 board with ads1115 to get the analog input.

You can find the calibration document in the FAQ option here:

However, it says the sensor is factory calibrated. Let’s see what seeedstudio suggests.

okay i undestood the part with the analog output now, but still i dont know how to calibrate.
The recommended modbus programm is not working correct or i cant use it.
Maybe anyone has experience?