my T used this on me once ... and it involved slowly introducing things related to what I was scared of and gradually increasing the intensity of the trigger (eg. in an example we looked at in a cbt book the illustration was fear of spiders so it went from seeing the word spider in a book, seeing a spider in a book, seeing a spider on tv crawling towards them, seeing a spider in a jar, touching a spider etc)

you might spend considerable time at each stage and while going through it practice a lot of self care and calming/grounding techniques and only progressing to the next stage when you feel completely safe with the current stage

as you go along the idea is you feel less fear and can better handle what you are exposed to as it becomes more familiar to you

from memory i was stuck on some stages for weeks; and only got to about stage 7 out of our proposed 10, which was still a massive difference to where I had started

with a child or young alter I think you'd want to go even more carefully again
the main thing is the idea is making it safer rather than retraumatising and to formulate the steps before hand and know it's ok to take time