Managing your anger does not mean forgiving or not taking action, it just means you have freedom to do it so on a rational basis rather than emotional. So you

Managing your anger does not mean forgiving or not taking action, it just means you have freedom to do it so on a rational basis rather than emotional. So you write your angry letter, burn it, then do what needs to be done, free from angry. It could be from a place of empathy: I wish you to be happy, but I wish you to be happy very far away from me. Or from a more selfish perspective, you simply want to know you did the best you could so that you don’t need to have any guilt on it.