The trigger mechanism was made from some scrap plywood. There are no critical dimensions but you can judge the size I used from the ruler in the pictures.
At the door end the lever catches the wire loop holding the door open
At the other end of the lever a vertical trigger holds the lever down until the rabbit pushed it back whilst trying to get at the food..
This releases the trigger allowing the leaver to flip up. and so releasing the door.
The door drops down sealing the exit and trapping the rabbit in the cage for later disposal.
That's all there is - Bate the trap with something tempting. Lift the door and snag the wire loop. Set the trigger, I like to ensure it is only just holding the lever so little contact sets it off.
Site the trap some where near the rabbit problem and make sure you check at least daily.
A trapped rabbit may jump around a bit so to prevent it overturning the trap you may like to put a stake each side to keep the trap stable.