Not a single webpage as of today on the Internet offers a way to delete learned words in GBoard (Google Keyboard app).
How can this be done without typing first few letters of a word and then when you see it as a suggestion, you long press it and drag it to the recycle bin icon in the middle of the screen. This is terribly inconvenient and there's no way you can remember all the words you've ever added or mistyped (GBoard remembers mistyped words as well).