Grove RS485 with modbus device and Pico WH

I’m new into physical computing and would appreciate all the help here…
I bought the Grove starter kit for Pico but I have challenges to program Pico WH that is connected with Grove RS485 via UART0 (Pin 0 & 1), the RS485 Modbus side is connected to a Modbus device where I want to read register from starting address 0x0100, it has modbus address 1. Can someone help me get started?
Some additional Modbs device data = Baudrate 19200; Parity : None; Stop bit: 1