He doesn’t, he prescribes spironolactone as an anti-androgen, and he made this as a general statement for all trans people (trans men as well as trans women). He’s just flat wrong, transitioning is actually associated with reduced risk of suicide, it’s choosing not to transition that increases risk for the most part. And you can’t control that you were born trans, he just treats it like a choice or a lifestyle, which shows an underlying ignorance about the biological causes of gender dysphoria.