The main reason you have gotten this far is that there is something wrong with the iris.
Grease from the helicoid sometimes contaminates the blades, preventing their free operation.
I do not recommend disassembling the iris further as it is fairly complicated to put back together.
Also, there is really nothing holding the assembly together. You need to keep the slottted plate up during transport.
What I do to clean an iris is to put the entire assembly (using a small, flat basket)into an ultrasonic cleaner with detergent and then rinse with distilled water, then rubbing alcohol to speed drying.
Do not use any solvent other than alcohol as the lower iris plate is plastic.
If you do not have an ultrasonic cleaner you can probably have a jeweler or watchmaker clean for you or the iris can be taken apart and cleaned with detergent distilled water and alcohol.
An alternate method of reassembly is shown at the end of the gallery.

No lubricant of any kind is used on automatic iris assemblies.