You need to configure two things:
1. Communication parameters:
Where you need to configure BaudRate, Word Length, Parity, Stop Bits and COM port.
2. Modbus Settings
Where you need to configure Modbus Registers.
MODSCAN address is your regular address + 1. So if you want to read register 18 you need to type 19 to the Address field.
Be sure that Device ID matches your device's Unit ID.
Length should be set to 1 and 03: Holding Registers set.
Check if it works.
If not, check you cabling, device or anything in between...