The thing to remember here is that wool has a working temperature of 80 - 150 Deg. C. This means that at approx. 80 degrees the fibers become plyable and at 150 they become damaged by the heat. At 299 deg. it scorches or chars and will ignite at 600 deg C.

The secret is that the temperature of steam is always the same. Unless under pressure steam is 100 deg C, or 212 deg. F. Right about the middle of the working range.

By using the steam alone to heat the fibers so that they will deform and create a crease and yet never get hot enough to damage the fibers.

I use my steam iron (which by the way is an industrial with a separate steam tank.) I can keep the sole plate of the iron at a lower temp and use just the steam to soften the fibers.

I then use the block as X Man showed to press the fibers into their new shape AND HOLD TILL THEY COOL!. My rule of thumb is two shots of steam to heat just hot enough that I can't put my hand down. Then press with a block of wood or a metal ruler acting as a heat sink to pull the heat back out of the wool till it is just warm. I should be able to put my hand down for a full 10 seconds without pain.

I have large tables that we use as pressing surfaces and we all press down till our feet come off the floor. That's 130 to 180 lbs of downward pressure. The time to cool is about 15-20 seconds.

2-3 seconds of steam to heat the wool.
5-8 seconds of pressure to set the crease while heating the next section.
Then move the pressure to the new heated section overlapping the first allowing the first to cool for at least 15-20 seconds before moving or disturbing the fabric.