The common advice to trade without emotion is bad advice. Emotion carries information and is involved in every decision, including good ones. What can be trained is the gap between feeling something and acting on it.
Three techniques carry most of the benefit. Naming the feeling reduces its intensity, which is affect-labelling. Reinterpreting the situation changes the feeling at its source, which is cognitive-reappraisal. And changing the physical state - breathing, standing up, leaving the desk - works when the first two are out of reach.
Suppression, the fourth option, is the one most traders use and the one that performs worst. Pushing a feeling down consumes attention, leaves the physiology running, and tends to produce a larger reaction later.
Related: affect-labelling, cognitive-reappraisal, box-breathing, tilt-protocol