I am remembering all of these thoughts from my past and I can't remember which ones are true. How do I stop ruminating??

Thank you so much. I just remember having this thought but I don't rememeber if I agreed with it or dismissed it or didn't care or said "no thats not true" and its eating away at me. That same thought came up a couple other times too I think and I feel like I may have treated it as real and not intrusive and I can't remember but I need to know :(