Never ever turn on the g.c. Replace the septum in the injector.
Spares are in the drawer beneath the g.c.
Loosen the vent cap under the left-hand front cover of the g.c. Open the helium cylinder, using the knob on top of the tank. You should not need to adjust any valves on the regulator. Open the air and hydrogen cylinders using the main cylinder knob of each. Again, you should not have to adjust the regulator or outlet knob.