How to use third adapter on Protector?

I want to use a dedicated adapter on two protectors for HA.

I’ve enabled three adapters

• first is WAN (behind another firewall)
• second is DMZ (not in use at the moment)
• third I want to use for HA

How can I configure this on the third adapter.

Cannot find the network settings.

It should be possible with a static routing: create a static routing on the new network card to the IP of the second Protector.