How to stop thinking about someone who hurt you?

Well the straight forward answer to the question is that You cannot plan on this. I am sure whoever has hurt you was special to you, and making him or her special wasn't a planned thing and it happened naturally with the course of time. It's an organic process of emotions being developed and not some project or goal that can be forgotten once it's over. You can fill any void in your life either be letting it go or by replacing someone. You don't need to forget that person, maybe just not give importance to that person anymore. I understand application is tough, but trying to forget makes you think about that person more. This might sound cliche, but Time does heal everything. Don't be idle, involve yourself in something more important and be occupied. Try healing someone which may help you heal yourself in the process. It's my personal experience, I couldn't forget that person, but definitely felt better when I was able to help someone else heal their emotional wounds. You develop a sense of being strong and being someone having substance in life.

The very first step you need to take is to cut all contact with them. No messages or calls or seeing them. Out of sight out of mind as the saying goes. Whenever you feel tempted to talk to them remind yourself of what they did to hurt you so that it puts you off contacting them. Don’t others speak about them infront or you and more importantly don’t ask around about the or stalk their social media. Try to keep yourself busy as the more free time you have the more your mind will wander. Remember if they’ve hurt you before they can do it and you’re worth so much more than that :)

You never have to stop thinking about it. Reflecting on pain is one thing, continually reinforcing and not addressing it is another. Changing the WAY you think about the pain and the person that caused it is what's most important. Forgiveness can be incredibly powerful and healing, but it's also a personal choice. Try to reframe your thoughts about the person and situation from "I'm hurt, they hurt me, I hate them" to "yes, I was hurt. I'm still hurting currently. But I am strong, I will heal, even if it takes time". You're in control of your life!