If you want to lock the iris at a fixed F-value (as I did), you don't need to remove the iris ring.

Take out the blade over the gear from its pin, turn it to have space and then you can remove the small plastic gear with small tweezers . Put back the blade on its pin.

I suggest to lock the iris ring with some small pieces of adhesive tape. You can see 3 of them in the 1st picture.

I decided to set the iris at around f:4. The fully open iris (f:2) has a diameter of around 13.5mm, so I closed it to 6.7 mm to get f:4 (I used a digital caliper to measure it) and then I locked the ring with some tape. In the 2nd picture you can see the final result.

If you don't need to remove the iris ring, you can stop here , go back and reassemble all parts. If you want or need to remove the iris ring, go further.