Now you free the meat from the bones. That is how you should think about it, freeing meat rather than slicing through it.
Start at the tail end by running the fillet knife away from you (toward where the head was) on the angle of the backbone. What I mean is that when you made your first cut in Step 5, you were on the top of the backbone. Now you run the knife over one side of the backbone.
Then you continue this process outward toward the edges of the fish, slipping the knife over the bones. It should require little or no effort, even for a large flatfish such as a halibut.
Once you get to the edge, pierce the skin with the knife and free it off the carcass entirely.
Do this on both sides.