How to Teach Siri Better Pronunciation
fieldguide.gizmodo.com/how-to-teach-siri-better-pronunciation-1776478700
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Launch Siri as usual, by pressing and holding the Home button or saying “hey Siri.” Then, say “learn to pronounce David Nield” or whatever the name is that Siri keeps getting wrong. Siri prompts you to say the name once and then gets a couple of attempts itself.