Forgiving is a personal decision, a personal journey. You don't necessarily need to tell the person you are forgiving that you are actually forgiving them or their actions, it all depends on the situation, on your choice and decision. It is something that you have to feel for yourself. No one can tell you what you need to do, no one can force you to forgive.
Forgiving is something that you do for yourself, to free yourself from a burden that you no longer need to carry for your highest good and for your own evolution. Forgiving can be part of your healing process, you are releasing low vibrational energies and emotions that you were holding within you and that were not serving you.
When you forgive, you are cutting the remaining etheric that were connecting you to the person in question. Forgiving is a process that takes place step by step, layer by layer, it can take time.
It is not always possible to forgive when someone's actions were too horrible... in this case, try to forgive yourself whatever you may reproach yourself with in this specific situation.
Let go of any thoughts and feelings of revenge, grudge or resentment because these things are only harming you:
1) when you wish evil on someone, it comes back to you in triple (even if it's someone who harmed you in the first place)
2) when you are holding grudges, resentment, etc. in yourself, you are keeping the connection and the etheric cord with the person who has harmed you and that's exactly what you want to avoid
3) these energies are low in terms of vibrations and they're not serving your highest good, they will not balance or compensate for the harm that was done to you
4) you can create karma for yourself and you definitely don't want the person who harmed you to be causing you to harm yourself more on top of the original harm that they caused.
Free yourself, heal these emotions. If you can, try to talk about it with that person. If it's not possible, you can talk to their soul in your mind (even if the person is still alive, it is possible).
If you are feeling stuck and feel that you can't move forward, try to seek help from someone. I'm here if you need, you can contact me.
Asking for help is not being weak, it is an act of strength and courage because it means that you are determined to feel better and to move on. The person who will be helping you will be showing you all the keys that you have within yourself and you will feel empowered.