Exerting pressure on your palate with your tongue, which stimulates growth in the jaw and acts on the maxilla, shifting it forward and up over time.
I’d love to see some actual evidence of that, which isn’t in the form of online anecdotes and testimonials on sites dedicated to the concept, or weird-as-hell “incel” sites. Something peer reviewed, in a respected journal would be a stsrt, even if the results haven’t been replicated yet.
Because it sounds like complete nonsense, and looking at the sites discussing it only reinforces my belief that it’s crap. I’ve spent some time searching for even a scrap of what someone with a hint of skepticism would consider compelling evidence and found nothing. I did find some communities I never knew existed, and wish I could now forget. Suffice it to say that “incels” are a truly strange bunch, and gullible at that.
Of course, my experience isn't peer reviewed, but it could play a part in motivating such research. After all, if society is in denial, they will not bother studying it, will they?