I don't think there's any way to simply answer that. Just persistent internal knowledge that wore away at me over years, with dissociation associated with living as a fake, constructed personality,
Truly, I never accepted myself as a woman until the last couple of years. I transitioned thinking it was just something I need to do for my mental health, but as I've let myself become more me I now know who I am. Probably in the same way that cis people just know who they are. My dysphoria had mostly gone. My dissociative feelings have gone. I now no longer feel like I'm an observer inside another person watching their life crash while I feel I'm missing out on my real life.
Anyway, I feel I've come full circle now. I don't think there's much mileage to be had in talking about one persons experience. While mine aren't untypical, they are just my experience.