Mark the location of the iris plate in relation to the helicoid casting by scratching a line or a fine felt tip pen.
This will allow you to replace the iris in the same position, as improper assembly will change the location of the actuator pin resulting in inaccurate f/stops.
Cut any sealing lacquer on the iris snap ring with an Exacto knife.
Using the previously fabricated tool, hook behind slot in snap ring and pull out one end.
Remove the snap ring. At this point do not turn over the lens as the iris assembly might fall out.

During reassembly a small dab of clear fingernail polish may be applied to the snap ring.
Allow to dry thoroughly before continuing.