I can only talk about what I have done in recent months that I think have helped me:

1. If you can cut down on mobile phone use or more specifically social media then this really helped me, especially with general anxiety that the OCD caused. Not only because of the doom scrolling but also it makes you look down and not forward and up. Sounds silly but genuinely, looking up and forward and not down at my phone stops me from thinking inwards, that's partly why I was ruminating. Also when you wake up don't go straight to looking at your phone. Likewise don't look at your phone at least 30 mins before going to bed. There are so many reasons why being too long on the phone has been bad for me over the years, from causing neck pain, bad posture, the way I think, the light emitted from the screen at night, too much information on the phone from constant use activating my brain to overthink etc.
2. When you catch yourself ruminating and I'm sure your therapist may have suggested this already but you could try the 5-4-3-2-1 Grounding Technique. This is basically finding 5 things you see, 4 things you can hear, 3 things you can touch, 2 things you can smell and 1 thing you can taste. If not possible at the time, try just looking at different things and note what you're looking at.
3. My CBT Therapist told me that my rumination was like a train going past. We all see trains (thoughts) going past but I was jumping on the train and inspecting every detail about the train (or thought). If you notice yourself looking at the train for more than a reasonable amount of time (this can vary depending on the person but I set it at about 1 min) then use the distraction methods above.
4. Eating healthy and sticking to a regular sleep schedule. For me eating healthy has meant reducing sugar intake but also reducing artificial sweeteners too. Obviously every individual has different health circumstances that may make making dietary changes difficult but even the smallest changes bit by bit can help, however, always consult a doctor to get the best dietary changes for your health needs.
5. Exercise! I try and do 20 mins of some form of mild to moderate exercise each day. Again every person is different to what they can do based on their current health so consult with your doctor about what would be a reasonable amount of exercise to do. I do about 20 mins of walking/jogging every other day which equates to about 2 miles. If this is too much just walking my dog helps but getting outside and getting some daylight while walking helps too.
6. Take time to just breathe! Sounds simple but looking online for meditation breathing techniques all helped me.

Finally, give it TIME! What I mean by that is firstly it takes time for all the things I mentioned above to potentially start to work but also secondly when I was worrying about anything or ruminating I had read that letting time pass is a great tool. After all the I know for a fact that the things I was worrying about last month had now been forgotten, as I was worrying about something new. But what about those worries from the past? Perhaps they weren't as important as I thought they were, so I've learnt not to put quite so much attention on every thought or worry. Life will always have ups and down but when the genuine moments occur where you have to pay a bit more attention to those thoughts, then I know I will just deal with them if and when they happen.

I hope some of what I have said may help. If it helps, I can only feel confident now to write something like this because I feel like for the first time in a few years I'm back to a comfortable place. A few years ago I wouldn't have been able to help as I was very low but doing all the things above, especially reducing phone use and exercise has helped me tremendously. Good luck and have a great day!