Meta, the best analogy I've heard is that your thinking brain is like a person riding an elephant. The elephant is your feeling brain. As long as the elephant is calm, and the rider is competent, the rider will be mostly in control. But as soon as the elephant gets upset, all the rider can do is hang on for dear life. Your feeling brain is older and stronger than your thinking brain. It's very, very hard to control your feeling brain with just thoughts. Usually to calm your feeling brain you need to speak its language, and calm yourself with sensations rather than thoughts. That's why it's more effective to listen to calming music or something than to just tell yourself you have no reason to be afraid.

From what I understand there are different ways of processing trauma, but all of them are about dual attention. In other words, you are feeling and remembering the trauma at the same time as you are keeping some of your awareness in the present where you are safe. How specifically you would do that depends on the particulat training of your T.