I’m not doing it for you, but will offer help.
You should already have your guide, but there is a lot in it
You can see more sample Modbus slave definitions, like you want to use in modbus.cfg, here
You should have everything you need to set up your first Modbus slave, apart from this part
Modbus numbers always come in 16-bit registers (words) over the protocol , but there are different ways to interpret 16-bit registers and/or combine them into e.g. 32-bit registers.
Looking at page 13/16 it suggests that reading one data value from the D&W is returned as 4 bytes, that is two 16-bit Modbus words, together representing a 32-bit signed integer.
I think the datatype your modbus slave requires will be 32 bit signed int. With that knowledge, you might find more mention of that fact in the manual.
Bearing in mind 32 bits is two Modbus words, you need to double the config length parameter - for your starter case to read one temperature, use length 2
Have a try, and show us what your modbus.cfg looks like