First, to understand why forgiveness is important we need to reflect on its purpose. To forgive is to overcome the negative emotions you feel toward someone or something, and no longer let that thing have power over your well-being. The underlying root of this is that something inside you hurts. You’re in pain because of something in your past and you need to rationalize that pain by attributing it to something else.
So what you must do before you externally forgive is you must internally accept. While I do want to remain respectful of any past traumas you may have experienced, you must recognize that your past is part of your life. It cannot be changed, and the best response you can have toward things that cannot be changed is to accept. This often involves finding meaning and purpose in the trauma or experience, because then it can be viewed as a necessary element to your growth and actualization rather than something that holds you back.
Basically, you must first forgive yourself and process your emotions before looking externally. Then at that point, if you feel like it’s important and productive, you can begin to forgive externally and relive those difficult emotions in a vulnerable way but with a new perspective and purpose behind it.