Most adults get worried that they are going to appear stupid if they make a mistake and so become nervous. Children don't seem to care. But the people who you are trying to speak to will understand if you make a mistake and will not mind at all. So you just have to do it anyway.

Do you have that feeling because of a previous negative experience? Perhaps you had to stand up in class and speak out loud? Maybe you made a mistake and the other students laughed? There is nothing to be scared of when chatting with English speakers. Maybe you could change the feeling of nervousness into a feeling of excitement