welcome to the forum oh,
Mike this is a great topic
My therapist and psychiatrist have never said "just let it go"
This is a skill or way to deal with the past that takes time while processing the emotions and flash backs.
I have posted a link to a website that has some information on mindfulness techniques on letting go, just one way to approach the problem.
True, that it must be done so a person can move on, we are all different so I expect we all move on and let go in different ways. As long as we do not suppress any longer, we will be alright
https://www.mindful.org/?s=letting+it+gopeace
Trina