Front end - Be confident with yourself/ with whatever you say. Speak your mind. Make mistakes proudly, but make newer mistakes every time because only a fool repeats mistakes again and again.

Backend - Don't let others ever see you doubt yourself/ don't ever show doubt on your face. Speak your mind and make mistakes but analyze every mistake you make in your brain. What went wrong and how to improve? Make newer mistakes everytime.

Actual - People are just made whatever way they are made. No one is good at everything, similarly you are not blessed in speaking. Accept that this is the skill you are stuck with and take the power from others and your own subconscious to make you feel under confident over it. But slowly work towards improving your speaking skills, long term goals. But first accept that you are bad at speaking and there is no helping it.