You start by figuring out where you are on a spectrum from Life to Death. The spectrum has these stages:
Love/Innocence > Separation > Sin > Guilt > Fear > Punishment/Suffering > Death.
On whatever issue you want to do forgiveness, or even just a general forgiveness, locate what you seem to be *most directly aware* of right now. For me this was "fear".
Whatever stage you are most aware of, thats the stage which has not yet fully "projected" into the next stage. And all the stages beneath it are currently unconscious. I was experiencing fear because separation/sin/guilt were unconscious and I hadn't yet entered punishment.
Once you've located where your conscious mind is at, work your way backwards through the stages to undo each layer of belief. If you don't need one or more of the earlier steps because you didn't find yourself in them at the beginning, you can skip them. e.g. if you mostly feel guilty, you probably don't need to undo fear.
At each layer of awareness/belief, there are a few steps to go through.
1) You believe that the step is real, and you need to undo this belief. Holy Spirit can help here. Recognize you believe in "real" this (e.g. real fear), and affirm that it is not real (e.g. "fear is not real, I am not afraid").
2) You should then start to have the insight that the only reason you are experiencing this step is because the step you didn't get to yet (unconscious) is CAUSING this step. Separation demands sin. Sin demands guilt. Guilt demands fear. Fear demands punishment. Punishment demands death. Therefore the step isn't there in its "own right", as an isolated 'thing'. It's a projection from another level and is being generated by another level. Seeing this helps you to realize the current level of belief is not the CAUSE of it. It is an EFFECT. And since it's not a cause, it is not real, so you can let it go. Undo the belief by affirming it is not REAL. "There is no real fear" "There is no real guilt" etc. Fear does not cause fear. Guilt does not cause guilt. Sin does not cause sin.
3) Once you can realize that your current level of awareness/belief (the stage you're at) is coming from a hidden level, and you undo the current level by cancelling the belief and the illusion that it was real in its own right, notice that if you do not correct the next level, it will REPRODUCE the experience that you just got done removing! You can remove fear, but if you don't remove guilt, it will reproduce fear. You can remove guilt, but if you don't remove sin, it will reproduce guilt and fear. We have to work our way ALL the way to the Atonement in order to uproot the whole problem.
4) Having undone belief that the current step is real, and affirming you do not believe in it, and having released it (Holy Spirit can help), your mind should have shifted to being aware of the next step/level. If you undid the belief properly, you will feel "free" of the step you were on, should no longer be experiencing it, and will become aware of the experience of the next step. So if you were feeling fear, you should no longer be feeling fear, and will now be feeling guilty. Guilt will be the main thing you are conscious of. Or whatever comes as the next level from where you're at.
5) Continue on through the steps this way until you get to the recognition that sin is not real, separation has not happened, and therefore you are IN the experience of the atonement. If you have undone the belief that the punishment is real, that the fear is real, that the guilt is real, and that the sin is real, and that the separation really happened, you should now be in the TRUTH.
The truth should make you aware of GOD. God's truth should be in some way in your mind, whereby you should now be able to ACCEPT that you are innocent, because you do not believe you sinned. You should be able to realize that you are forgiven, because you did not really do anything. And you should be aware that God still LOVES YOU 100% because you are WORTHY of love, having not done anything wrong.
You may find yourself feeling "I AM FREE". You may experience JOY. You should feel RELIEF. Especially now that you can affirm "I have not sinned, I am innocent". Your mind is now experiencing the truth as your primary, conscious experience. Forgiveness accomplished. And because this has been ACCEPTED and OWNED, and because you've seen through all the illusory levels of the ego thought system, you are now PERMANENTLY FREE of what you forgave. It will not come back, because it has no foundation. The Atonement principle has completely undone the "cause" at its roots.
Your mind is now IN a state of forgiveness. You are in the Holy Spirit. You are now the light of the world. You are the Prodigal Son, and you've come Home!