Short term: Distraction; Long term: Therapy
Trying to make yourself stop thinking about an event only makes it more likely to happen because you constantly need to reference it to tell yourself what not to think about. For instance, telling yourself not to think about a yellow jeep will make you think about yellow jeeps even if you haven't thought about one all day. But you can learn to process how you feel about an event so that thinking about it no longer causes you distress. Empirically based treatments like Cognitive Processing Therapy and Prolonged Exposure are meant to do this - be able to be in touch with a memory without being upset by it. Unfortunately, there is no way to get rid of memories.