This had been a really positive addition to my life recently, because of my horrific memory loss (a common symptom of depression and probably my least favourite). The good news is I'm really great at remembering anxiety-inducing stuff and regurgitating it over and over until I end up in a spiral? REALLY. GREAT.
Take a positive subject from your life (right now for me this is travel but it can be anything you really enjoy/enjoyed - food, gardening, films, sports, music, fashion, etc) and keep a diary from memory. You can draw pictures or diagrams, or leave blank spaces to fill in with names if you can't recall them.
I started doing this with a massive roadtrip I took in New Zealand with my family ten years ago, in a pre-instagram lifetime. I charted out the route we took, and then tried to fill in the gaps - where we stayed, what we did there, what I ate, what I saw, who I met, what I bought. The journalling process was very restorative and really helped me access positive (but forgotten) memories.
Next I did it with other trips. Now I do it every few days and it's actually helping me remember people and instances from positive times in my life. I normally experience the same repetitive thoughts over and over, so this has been a good exercise for me.
If you try it, let me know how it goes.