If he is only triggering 1 amp then just set what ever input he is using to turn on trigger #1 and run the cable from trigger 1 to the amp.
If he is turning on 2 amps then you can either daisy chain a trigger cable from one amp, assuming it has a trigger out jack, to the other or you can run a separate trigger cable to the 2nd amp.
You can set up each input to either use one trigger out or both.
Hope this helps.