Coaches have mapped the exact moves that read as confidence:

• Downward inflection — let your pitch fall on the last word. Drop, and it sounds decided. Rise, and it sounds like a question
• Steady pace — fast reads as nervous, crawling reads as unsure; aim for the calm middle
• Held volume — confident speakers keep volume level instead of fading out by the end of a sentence
• Placed pauses — a beat before a key point signals control and makes the next words land harder

None of this is personality. It is technique. Plenty of quiet, introverted people build a commanding voice through plain practice.