how to disassemble Rowenta steam iron?

The plastic molded part into which the water is poured pulls out, and beneath it is the screw.

First make sure it is not plugged in.

Next remove the back plate, there is a single torx style screw. Once it is removed the rear plate will pop off if you pry gently on alternate sides.

Once the back is off you will see a black plug with two heavy grey wires (power wires) and a smaller red, black, and blue wire. The entire plug assembly will slide out to the rear with a little pulling. It exposes two leads from the base plate, freeing up the base plate for later removal.

There is a small white plug leading to two white wires at the top of the transparent box that holds the electronics. It also comes out to the rear with some gentle pulling. One this is released it will allow the base plate to be separated.

Now you can remove the base plate by removing the stainless cover at the front of the iron - it pops off. This exposes another torx screw.

The other two screws that hold the bases plate are at the rear of the bottom of the iron. When they are removed the iron base plate will separate from the plastic body.

Finally, to remove the transparent electronics box you must first lift out the temperature control. It lifts our with gentle pressure, but when it comes out a small spring and indexing pointer can pop out of the plastic arm that remains below the dial. Do not lose this part.

Once the dial is removed the plastic box containing the electronics will slide out of the iron to the rear.

Be very slow, gentle and do it with lots of patience.

Putting it back together assumes you have been careful and paid attention as it came apart -

Apart from the obvious two rear screws which you access by removing the plate on the power cord side, there is a "hidden" front screw just at the front of the lower part of the handle/body.
You can access that screw by pulling out (towards the front of the iron) the piece of plastic which is used as the water inlet to the tank.
That piece stays in place using an O-ring at the bottom side and a slot/grove on its top.
Once the front screw has been removed, everything else becomes obvious.