If you make the same typo often enough and don’t correct it with the autocorrect feature (eg backspacing or jumping to the wrong character instead) Gboard will think it’s what you’re meaning to type and add it to your dictionary. When it comes up in the little autocorrect thing above your keyboard, you can drag it into the trash. You could also go through your dictionary and delete specific words as well. That’s what works for me anyways, not sure if I’m correct