What would believing in yourself change today? Perhaps you would share the first version. Ask the question. Say no. I want self-belief to become a decision I can act on.
Name the thing you have been putting off. It might be asking a question, sharing a first version or saying that you cannot take on another commitment. Decide what the first attempt actually involves and what you can reasonably put into it.
The risk does not have to be dramatic. You can begin with a step whose consequences you understand. Self-belief is not a reason to ignore what you do not know; it can be a reason to find out instead of staying still.
After the attempt, separate what happened from the story you tell about yourself. Which part worked? What needs practice or a different approach? One awkward conversation or rejected idea does not have to become a verdict on your ability.
A boundary belongs here too. Believing in yourself can mean saying no, asking for time or choosing another direction. For me, the value of self-belief is in that movement from waiting towards a considered choice. Give it a shape you can recognise in your next action.