Please look in the datasheet that can be downloaded from the CODESYS store along with the software. In there are instructions for accessing channels in groups 2 and 3. Basically you created channels as you would in a standard codesys modbus device (although all registers and coils are identified by name. You then map these into your application. There are a number of utility function blocks in the library that may be helpful.
Group 1 is the same across all Neuron devices, so I created the drivers to automatically create channels and map the data into an automatically created function block. If users find this helpful then I could do the same for the other groups. I would be interested to hear if users find this automated mapping helpful, or if they prefer to map the channels used themselves.