NLP is not a therapeutic process, and isn’t a psychological approach. It is a way of enhancing your resourcefulness and enjoying life. If someone is interested to discover how NLP is used, they can find so in many, many ways.
One such way is personal development. I’ve found NLP to be a great skill in developing better relationships by understanding how people communicate, for example.
In this case, how can you deal with someone who is quick tempered? The simple way to find out is to know that person well. Identify the triggers to that behavior. Very often, quick temper is triggered off by a variety of factors. Your job, if using NLP, is to look for resourceful emotions to completely counteract those (we call that collapsing anchors).
