How do I come out as asexual without people thinking something must have happened (hormonal, trauma, etc) to me?

The best way to just say it is that you're asexual, and you were born that way! While you may have identified as something else in the past, it doesn't mean anything has changed with you, just that you realized that you identified as asexual and that it took time to understand it and come to terms with it!

step 1: acceptance. What pleases you or doesn't please you is your business. step 2: Eye for eye. Tell people to mind their business. Step 3: pursue your fantasies. Everything doesn't start and end with sex. And I think you're great! :)

You don't have to explain why you're asexual. Just say you're asexual, but overall it doesn't actually matter if you identify as such. You aren't planning to date them anyways

You could always just tell them. Ask if they have any questions and clear some things up like how youre perfectly fine.

simple if you feel that it is right just do it, you have nothing to prove ,just say that it's who you are and they can't change that or you

If your refusal of sex has a traumatic origin, it is probably something you should take care of with some professional help to support you. Asexuality is simply a sexual orientation that has no specific physical or traumatic origin, people just aren't interested in sex, without a specific "cause", just like the sexual orientation towards one specific gender or more has no specific cause, but is simply something innate. If you feel like something caused your lack of interest in sex, you should probably take care of this "origin" first, to realize if you're really asexual or just psychologically blocked towards sex, and then deal with what you find out.