You need special firmware, all of which is explained on the RCExplorer forum, but.....the triflight extensions are not built into the revolution target (I believe that's the target you used).
I've never used the revolution target, nor any of the Omnibus boards, but it looks like the revolution timer bank layout should support tricopter operation. I don't see a free ADC pin for the servo feedback though, which kind of defeats the purpose of triflight.
I'll dig a little deeper and see if there's anything possible for that target. While a little late now, the KakuteF4V2 or one of the Matek405 boards would have been a better choice.....
Would love to see more details of your build, always wanted to build a large tricopter.
EDIT: There is an RSSI pin, but it's not clear which port/pin it is. The port/pin defined in betaflight is used as a pwm output pin in dRonin. I'm not sure how compatible this board is even though it does appear to run given this, and other differences, I see in the target files.