The last two (top row, the two to the right of the center larger gap) hatches will need to be connected to the microcline lever in the meeting area when there is room in the queue. Once all hatch connections are complete, the next levers are in the little alcove off the exit of the trap. The middle lever opens the magma floodgate and the top opens the bridges array (bottom one for expansion). Open both, let the system fill completely then close both. Only use the microcline main lever after the magma is full.