Hugs.
My understanding of forgiveness is that its not linear. Painful memories, flashbacks, still pop up.
Honestly though, I myself don't have a good grasp on what forgiveness actually is.
Maybe consider getting a book on forgiveness. Like "Forgivness: how to make peace with your past and get on with your life" by Simon (last name).
In my own experience with coping with flashbacks and bad memories that hit me out of nowhere, I am coming to accept that some things, I cannot change, and I am changed because if them.
I wonder if you might need to process through some of what you've experienced, before you can forgive.
Another thing, I keep hearing about how forgiveness is about letting go and that Its not about saying "it's ok." Because its not ok.
Anyway, this is no step by step, but I hope I helped.