Yes you can sometimes train your brain to forget things just like you can train your brain to remember things.
The way you train your brain to forget about things is to repeatedly stop thinking about those things and try thinking about new things and better things.
Eventually you should be able to forget the things that happened in the past to you.
However sometimes memories such as bad memories can stay in your brain forever but you can still try to put it out of your mind at least for awhile.
But if you keep thinking about new and happier thoughts then you may stop thinking about that event that happened to you but it might take several years for it to happen.