Any tips to stop ruminating?

Rumination is very hard because it can sneak up on us unbeknownst to us. What I will do when I catch myself ruminating is I will go for a walk or do something that distracts my mind without trying to push the obsession from my mind (that’s the hardest part). I make a decision that I am not going to let ocd rule the day and I get busy and if the ocd stays I don’t care. I let the ocd do it’s thing. This takes a lot of practice and I am not always good at catching it but I keep trying. I hope this helps.

To fix the problem of rumination, you have to be aware that you're doing it. Your first step to stop ruminating will be to build the awareness to when you are ruminating and stop it in its tracks. When you catch yourself ruminating, simply say "This is rumination, it is not helpful". Anytime you catch yourself in your head, say this phrase and then try and focus your attention on something more meaningful.

Dr Michael Greenberg wrote some articles about ruminating that you might find helpful

I highly recommend Nathan Peterson's videos. He is a licensed therapist and has a channel titled "OCD and Anxiety". He's done some community posts on rumination and a video on it.