If you want to remove the iris ring, you need a lot of care and patience. You have to take out the 9 (!) iris blades from the pins , and turn them as shown in the 1st picture. They stay attached to the ring, but you have to move them very carefully.

The ring can come out only if turned fully in one direction, until it stops, then it can come out. I think it has to be turned counterclockwise, but I am not 100% sure. Try both, in case.

When you will mount the iris back, you have to insert the blades on the pin. The blades will mix one on eachother, and you wll need several trials to find the correct positins of the blades. Look at pictures in Step 8 to see whch is the final result that you have to get. This step was quite tricky for me, a lot of care and patience is needed.