Hi Uday,
Discovery checks SNMP OIDs stored into SNMP System OIDs table within ServiceNow to correctly classify the device & update the Manufacturer & Model ID. In your case, i think SNMP OID of your device is not added into SNMP System OIDs table. You need to add it & provide the Manufacturer & Model ID detail in it as well. So next time when you run the discovery, it will populate correct data as required.
