By a wide margin the least difficult method for sharpening a knife (filet blades included), is to utilize an electric sharpener.
Most of sharpeners will have something like 2 phases, one for sharpening (and really eliminating steel from the edge), the other for cautiously sharpening.
Whatever model electric sharpener you own (or expect to purchase) the standards are something very similar.
You should threaten to use the knife-edge through the sharpening stage (which is generally a flimsy opening on the highest point of the sharpener), for the quantity of passes it takes to arrive at the necessary sharpness.