There are two ways to add a MIB variable to the Known OIDs dropdown list.

1. When adding a new SNMP MIB Object (TLV 11) in the GUI with an unknown OID/text combination, a popup will appear asking you whether you want to add that OID to the database. Clicking 'Yes' will add that OID/text combination permanently to the Known OIDs list.
2. A more convenient way to add multiple OIDs to the Known OIDs list, is to edit the MIBS.INI file located in the installation directory. Check the "Conguration of the SNMP OID translation database - MIBS.INI" section of the manual for details.