Arduino uno -----> Modbus ----> HMI

Hi

I am trying to make a little project.
I have a sensor that I connect to arduino uno and delivers asynchronous serial data in TTL RS-232 format (through pin 2 and 3).
See https://www.atlas-scientific.com/_files/_datasheets/_circuit/FLO-30_1.4.pdf

I want to transfer this data into my HMI through Modbus 485 RTU.
I have been looking at some codes and libraries and am getting a little bit confused :~

I tested some examples on my arduino and connected it to RS-485/usb to computer using program "Baseblock MODBUS RTU communication tester" but no luck.

Can someone help me with this....
Like if we start simple and I wanted to send the number 25 from my arduino through modbus and see it in my "test" program, what do I do. ?

Regards.
Steini

How did you connect to that RS-485/USB and to the computer? Provide wiring information/photograph.