Believe I am, I can
Start with saying "I can" once a day. Before important events, try saying "I can" every 15 minutes.
When you've mastered that, (how does it make you feel?), move on to chanting "I AM" with full force and without deviation and with believable authority. Picture to yourself your will and authority filling the room or area or building as you say it and tense your muscles a bit.
See yourself as a glowing being and god of your own universe, if it suits you at the time. 😁