Some of our waters require single (and sometimes barbless) hooks on our lures. In addition a single hook can hold fish better and makes releasing native fish easier.
However lure manufactures insist on selling their lures with treble hooks installed.
It is pretty easy to convert a salmon plug to have single hooks. Many have instructions & replacement hook suggestions printed on their packaging.
First remove the treble hooks, by opening the split ring and working it off the eye attached to the plug.
Next select a single hook to replace the treble. A good rule of thumb is a siwash hook that has a gap that is 50% larger than the gap of a single hook of the treble. More about that is explained here.
It is often good to drop the hook back a little bit father by adding a bead chain between the plug and the hook.
Clamp the eye of the hook around one end of the bead chain. Then use a split ring to attach the bead chain to the plug. Usually the hook is placed on the belly eye.
The result should look like this.