I know a little bit about rumination. For me it was more like trying to "capture" something...ideas and dreams or other concrete information, but also like a general feeling or mood of something like a memory, experience, etc. Not sure if that's what you're talking about, but maybe similar.

Journaling is a helpful practice for all kinds of problems for many people. I know it has helped me. You can record inspirations, things that are bothering you to just work them out like you might do with another person, vent frustrations, etc. I think it's also good to put in the happy stuff too. Sometimes it may be "unimportant," but if you're afraid of losing it then there's no harm in writing about it. I have written tons of stuff that is basically just ink on paper, nothing more, but trivial as it is, it helped at the time which is what's important. Plus, if you are receiving any treatment, it's helpful in tracking your progress.

Other ideas are meditation, visualizing letting go of thoughts, or simply getting lost in something else that can distract your mind (book, video game, binge-watch TV show...) Hopefully some of this is helpful