Does that book actually adequately describe that gender is known to be a clinical thing, not something in the mind? That is, it's immutable. You can alter your sex, but you cannot alter your gender. Some people also understand easily when I say "well, if some evil witch was to now magically change your body to [male|female] one, you'd surely do all in your power to undo that. You would feel extremely uncomfortable and you would keep feeling uncomfortable until the ailment is over. You wouldn't want to live in the [male|female] body, you'd want your own back. And that's how it goes with me as well, just like with you."

The cis people I've talked to about this seem astonishingly able to imagine how disgusting it would feel for them to have to suddenly live in the body that has the wrong sex. Of course, being transgender is somewhat hereditary, meaning that it's possible that one of your parents might not really relate with the "you would feel discomfort in a body of the other sex, right?" thing, because a parent of a trans person may very well be an egg.

I mean, definitely make them read the Dysphoria Bible, it will definitely not do anything bad if they do, but for what I remember of it, it's targeted more for people who are already receptive to its message, not so much for people who might have some defense mechanisms protecting from getting the message from it. So, some emphasising of these things might be of use? (Or maybe I just remember that book a little wrong? :) )

Would you mind sending that to me, please?

Edit: is this it? https://genderdysphoria.fyi/en/what-is-gender