Self-confidence doesn't come from repeating a positive phrase in front of a mirror.
It arises from evidence.
You face a difficult conversation and manage to position yourself better.
He gives a presentation and realizes he was clearer.
Record a video that you would have previously avoided.
Organize your thoughts and finally manage to say what you wanted to say.
Each of these small experiences gradually changes the way you perceive yourself.
Therefore, improving communication goes far beyond learning techniques. It's also about starting to realize, in practice, that you can do it.
The story you tell about your communication changes when you begin to notice its evolution.