How to not dwell on the past?

I have this tendency of mentally going over events in the past (both good and bad) & I know it’s something I shouldn’t indulge in but can’t seem to help it. For a while I just assumed it’s just an aspect of my character – being an introvert and history-lover etc. but I seem to be doing it more these days esp. after someone I loved died a year ago. How do I keep my focus consistently on living life looking forward?

BTW this isn’t a disguised cry for help – I’m self-aware enough to be able to observe my own tendencies; I just need help with ideas on developing better mental discipline and being consistent