If the cap is made out of cast steel, it should bend without heat.
Just don't overdo it.
Each time it is bent, the steel will become more brittle.
The brittleness can be reduced by annealing it but this should only be needed after it has been bent a few times.
The steel casting was allowed to cool slowly so it should already be annealed when it is new.
To anneal steel, it needs to be heated up to a bright red color and then slowly cooled to room temperature. Do not be tempted to speed up the cooling by using water or oil.