This excerpt is from one of PC's archived articles on how to stop rumination:

How To Reduce Rumination

According to Nolen-Hoeksema, there are essentially two steps to stop or minimize rumination.

1. Engage in activities that foster positive thoughts. “You need to engage in activities that can fill your mind with other thoughts, preferably positive thoughts,” she said.

That could be anything from a favorite physical activity to a hobby to meditation to prayer. “The main thing is to get your mind off your ruminations for a time so they die out and don’t have a grip on your mind,” she advised.

2. Problem-solve. People who ruminate not only replay situations in their head, they also focus on abstract questions, such as, “Why do these things happen to me?” and “What’s wrong with me that I can’t cope?” Nolen-Hoeksema said.

Even if they consider solving the situation, they conclude that “there is nothing they can do about it.”

Instead, when you can think clearly, “identify at least one concrete thing you could do to overcome the problem(s) you are ruminating about.” For instance, if you’re uneasy about a situation at work, commit to calling a close friend so you can brainstorm solutions.

Positive Self-Reflection

Nolen-Hoeksema has also studied the opposite of rumination: adaptive self-reflection. When people practice adaptive self-reflection, they focus on the concrete parts of a situation and the improvements they can make.

For instance, a person may wonder, “What exactly did my boss say to me that upset me so much yesterday?” and then come up with, “I could ask my boss to talk with me about how I could get a better performance evaluation,” Nolen-Hoeksema said.

From this article:
https://psychcentral.com/blog/why-ru...d-how-to-stop/