Modbus connectivity issues


I am trying to connect three gas flow meters to my laptop through modbus. When I connect the first meter, it gives a 'Time out" error, also I am not able to communicate with the device, i.e. not sure how I command it to let gas flow through. The user manual with the device is useless since its in a different language and the manufacturer has not yet responded my request for an English version.

any guideline will be much appreciated.