Their "theory", from what I have gleaned from many troons, is basically that every cell in your body has a state corresponding to your gender controlled by your hormones that started with puberty, so if you stop T and inject a bunch of E, all the cells will flip over to female, once this reaches critical mass your body is now female and starts readjusting itself to be female even though this has never happened for anyone ever. (And nobody seems to ever explain why we would think this should happen at all.) Some, like Jake Alley (my favorite but not the only one), believe this will cause your genitals to stop being "inside out" at some point even though this has never happened for anyone ever, they regard surgeries as merely "correcting" some minor mistakes. This isn't a falsifiable hypothesis (even though, again, it's never happened for anyone ever) because the premises aren't true in the first place lol
Also, don't you dare say any of this sounds like a soul, this is science, buster.