How do you forget a person?

I had an intense crush on a person with whom I used to go to learn German. I knew I could only learn the first level of German, and that I would not have time for the next levels, so I had only three months with her. We had good conversations and decent chats. I didn’t even know the person existed three months ago, but I was enamored by her. Towards the end of the course, which was the only avenue where we met, I thought I might as well ask her out. However, I got rejected. It has now been two weeks, and I’ve been trying to do all the things that people suggest: going out with friends, doing things I enjoy, and so on. But whenever I have those five minutes of downtime, the person pops up in my mind. Also, most of the time when I wake up, for some reason, the person comes to mind. Is there any remedy for this?