In order to relieve stress you need, firstly, to calm down and try to get distracted from tense thoughts. Get your mind involved in some pleasant and enjoyable themes, which you like most. As for me, they are memories about summer walks in an open air with my friends. Secondly, you need to admit that you are in stress, you are scared to say or to do something, and then just try to overcome such an obstacle persuading your mind that it's normal, all the creatures are afraid of sth/sb and experience some stress, so you needn't to be overwhelmed with this stress because it's unnecessary. In the end, you will become more confident and your brain will be in peace. I do so for my whole life and it also help me. Since I've started to follow such soothing methods I've already become more self-assertive and boosted my self-esteem visibly.