For pressing you need three things:
- Heat
- Moisture
- Pressure
So plenty of steam to loosen the fibers and good pressure to press them into the new crease.
For truly the sharpest crease, follow the iron with something heavy and cold (I have multiple old flat irons which I use - we’re not talking about several Kg; just something which will keep the fabric pressed flat). Press with iron, then replace with the heavy object until the fabic has cooled.