SNMP Trap Alert rule / Template

Hi,

I am trying to configure alerts from a firewall via snmp trap.

I have configured snmptrap service on librenms server.

Librenms receives the alerts generated by a firewall in traps.log

I have created an alert rule and I receive the notification by mail.

How can I configure it to generate an alert when it receives a trap due to a port drop, for example?
Where can I find a list of variables to use?

Thanks!