How do I change my personality?

I need to be more confident in professional social situations. Things like interviews etc. I'm too nervy. How do I stop? In high pressure situations I tend to get a fight or flight response and I need to manage it. Unless I have time to sit down and think about something, I tend to use a lot of filler phrases and can't communicate ideas properly.

There's a good chance I need to step into a sales role to earn anything more than minimum wage with how the job market is. Has anyone got experience with doing this?

I also need to change my mindset about work somehow. I struggle to motivate myself unless I'm passionate about something. How can I be happy doing something I hate?

I feel like my whole brain needs rewiring.