Step by step guide for making NPC faces available as Tav presets?

[PoetryInMotion]

Hi everyone! Very new to this modding thing, but, as the title suggests, I'm trying to do something that shouldn't require too much tweaking...

I know that I can find what I'm looking for on Nexus etc., but would anyone be so kind as to make a quick guide on how to make new presets using unique NPC faces (say Astarion for body type 2 Elves), so that I can get around to it on my own?

--> In this instance, I know that there is Mizora has a human face somewhere in the game files, that I would like to use for a body type 1 human Tav. Might an expert narrow down the steps for me please?

Thanks a lot.