All relevant product literature can be found on the Analox Sensor Technology website from the obsolete products page. Here you will find the LC Commercial datasheet, hardware manual and software manual.
This applies to not only the 3000SI series of sensors, but also to any loop powered 4-20mA output sensor.
Within the hardware manual locate the 'Analox Ltd gas detectors section under 'Input configuration'. This section details the connection of the negative (-Ve) and positive (+Ve) wires of your 3000SI device.
It may be necessary to set the jumpers on your device (As detailed in the document) however if you have ordered this from Analox as a system the device should come with the jumpers pre-set.
Once the sensor is connected to the panel and power is applied, refer to the software manual for guidance on calibrating your unit and setting units of measure. Look out for the helpful map on page 4-9.