Just a moment...
Even if the camera is in manual iris mode, sometimes changing the iris won't result in the actual exposure changing. Why? Because the camera has other methods of maintaining or setting automatic exposure, and if those are active, they may cancel out your iris changing. Watch out for automatic gain control, and automatic shutter control. Typically the shutter is the culprit; if you don't see the shutter speed actively displayed (i.e., "1/60" in the lower right of the screen) then there's a very good chance the shutter is in automatic mode! When the shutter is in auto, it will change on its own, without your guidance and perhaps without your approval.
To get the shutter back in manual mode, press the SHUTTER button.
To get the gain back in manual mode, ensure that the AUTO/MANU switch is in "manual", and check the settings for the Gain Switch: if any of the gain switch's positions are set to AGC, and the gain switch is set to that position, then the camera will be operating in automatic gain mode. Either change the gain switch's settings, or change the values assigned to the gain switch to eliminate the possibility of automatic gain.
For true manual exposure, you have to ensure that automatic gain and automatic shutter and automatic iris are all disabled, and that all of those functions are instead operating in manual mode.