Emotions are not controllable or choosable but our reactions to them are trainable. One good technique for this is mindfully observing and labelling the emotion until it goes away; not trying to change it but also not acting on it. With practice one can observe the emotion subsiding within a minute or so. This, eventually, leads to less emotional reaction overall because we're taking away the habitual pattern of the mind to constantly react to everything it likes or dislikes.