Since we are all victims of victims, most dark spots come from childhood. You will often find your client back at their old house or apartment. Get them to describe the scene. How old are they?
Then ask, "What is happening? Are you alone?" If your client shows distress, you can have them go above the scene and look down, but it is better if they stay in it. Allow them time to see what is happening.
Ask the client to describe what they are feeling. Then ask whether it feels new or familiar. If the feeling is new, start there. If it feels familiar, they have felt it earlier — have them go to that earlier moment. Keep asking new or familiar until you are confident they are in the scene of the first time they felt that way.
Have them describe the feeling and feel it as deeply as they can. It will naturally subside. Tell them you will stay quiet while they feel it fully, and to let you know when it has subsided so you can continue.
Once the pain has been released, have your client imagine going into the scene as the adult they are now. Here the adult can see the entire scene from a different, more mature perspective. Allow them to confront the person who has wronged them and say whatever they want to say — yell, scream, curse, whatever they need to get it out.
"Here is your chance. You may say whatever you want and don't worry if you want to curse, that is fine with me." Even if the other person is deceased, that is okay. Tell them off. Your subconscious mind will see it as fact.
Many clients want to hurt them — beat them up, punch or kick them — and that is alright. However, do not let them kill them just yet. There is still work to be done with them.
Once they have said everything they wanted to, it is time to tell that person how they made them feel and how it affected them their entire life — why their actions caused shame, not-worthy, not-good-enough, why their behavior made them miss opportunities and make stupid decisions which cost them their happiness. Feel free to call them out. This is very important toward releasing it.
Once your client has spilled their guts, allow the other person time to apologize or explain themselves. It may be that they were victims of victims too. Here your client may learn something about that person's childhood they did not know. Many times clients will see their assailants crying and apologizing. This is very healing. It is up to your client to accept the apology or not — some people are too narcissistic to apologize, and there is nothing you can do about that.
Then cut the cords. Each cord holds a negative emotion. Go through each cord and make sure it actually cuts. If it does not cut all the way through, someone still needs to express a feeling or thought. Continue until all the cords are cut.
Practice
Practice the new-or-familiar bridge on yourself with a current emotional reaction, and land on the earliest scene it points to.