1> Don't message the person,
2> Don't replied to his/her message ,
3> Don't save his/her number on phone,
4> Don't save his/her number on head,
5> erase anything that has to do with his/her, example his/her photos.
6> Don't have him/her on your
social media.
7> say to yourself I don't want to remember this person, and your body understand everything you speak to yourself.
That for my own experience. It happen to me before and that is what I did to forgot the person.