As far as I know it's in the tutorial they insist you do upon first enabling swiping

edit: Don't actually see a tutorial in the app. Maybe I'm confused with another app such as Swype, but the same technique seems to apply to all.

I'm pretty sure Swype did explain it, and I know SwiftKey has this gesture as well (though I don't remember if it was ever explained to the user or just assumed they'd remember it from Swype).

The default keyboard on my Android didn't have any such tutorial. I did look in the app and online.

Swype taught me, it has helpful tips and I still use their keyboard to this day

Swipe style keyboard? How does that effect spelling ? So confused - I get how it changes to "predict," anticipate or whatever the AI engineers say but what I don't understand is changing a real word to a non-word. That's not intelligence. That's something else and I don't know what they get from changing word to a misspelled and nonexistent word other than eventually driving the human race insane: I'm going to be a Luddite;

Er, "son" and "soon" are both real dictionary words. Swipe-style keyboards use an internal dictionary to find the most likely match to the swiped pattern, and have methods for adding new words (mine for example automatically adds any tapped-out words after you hit space).