I agree with asking your provider for the best answer, but I will give some general tips that I've learned in ERP to manage my own ruminating compulsions (that's one of my biggest ones as well).
Try not to intentionally bring the thoughts to mind, but respond with ERP techniques when they "randomly" pop into your head as you go about your day. So when the time comes that a distressing intrusive thought crosses your mind, then focus on acknowledging the thought, acknowledging that it is uncomfortable/distressing/disturbing, remind yourself that thoughts are just thoughts (not facts), and you get to decide whether that thought deserves your time.
Don't try to gain reassurance, and that includes resisting the urge to analyze and reason against the thought if you struggle with that (that is something I personally deal with, so it might not be the same for you).
Another thing I recommend is trying to stop yourself if you feel the rabbit hole spiral happening and take a step back to ask "is this OCD/an intrusive thought? Is it a legitimate issue that requires my immediate focus?" I have found that it helps to tell myself things along the lines of, "I have OCD. This is what it does and how it affects my mental health. It wants to protect these things I value highly by causing extreme anxiety over thoughts."
And one last thing is that I like to finish off whatever strategy with asking myself what is the next most productive step I can take in the moment in getting my goals done, however big or small. And I get to decide what that next most productive thing is, whether that is working on a project, starting a chore, taking my dog out, brushing my teeth, playing a game to relax, going to bed, or drinking some more water (self care and maintenance is very important). I think it's effective to get in the habit of re-orienting myself after dealing with OCD in any capacity -- from using a quick "sit with the discomfort and choose to move on" tactic on an intrusive thought to recovering from an extended meltdown.
Remember, ERP is awesome and I highly recommend, but it is something that is not perfectly easy, and it takes work. If you find yourself struggling with it, do not get discouraged, do not be hard on yourself. It will get easier, you will get better, and it will be a lot easier if you are patient, kind, and compassionate with yourself. I know it's very difficult for many people with OCD (and any mental health struggle for that matter) to be nice to themselves. We often want to get frustrated with ourselves and put ourselves down for not being "normal." Societal conditioning has made us look down upon any form of struggle, including mental health issues. You are allowed to not be "perfect," whatever that is. You are human. You deserve support and compassion, especially from yourself. Be proud of yourself for any amount of progress, even if it seems small. You're doing well already, give yourself credit for taking these very scary and very big steps.
Best of luck! :)
