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I gave them a letter explaining how i felt

Just be honest with them. Parents should love you for who you are, not for who you love or how you feel. You could say "Mom/Dad, I need to talk to you for a moment." and then tell that parent. Your parents might talk for a bit about this, and it could be to discuss if they accept it. They should accept it, as they are your family. If they don't, then there should be people who can accept you. Just be you.

Start off by giving subtle hints, then make those hints larger and larger until you're comfortable to come out to them.

Looked here to see if I could also find advice. Perfect. Subtlety is my specialty.

My friend told his mom who is less aggressive first, I recommend telling the least aggressive parent

Ask questions, kinda scope it out before you come out to your parents. Like "so, what do you think of trans people? What about gay people?" etc. Be VERY casual, you dont need to ask them rapid fire. Just stay calm, and until you're sure it's safe then come out.

Ask if they support lgbtqia+ first if they say yes then tell them you're trans but if they say no or something completely bad about it don't tell them