As noted, the problem here is the knife steel is probably in a hardened state — in order to work with it you would want to anneal it, which would then allow machining it more easily, then re-temper the blade, restoring the hardness. This would require knowing the steel alloy so that one would know the correct temperatures and times, as well as an oven/kiln able to reach the requisite temperatures.
Folks have been successful w/ steel alloys which are suited to machining on a small-scale:
It’s not possible to just take a very shallow pass because that would result in the tool rubbing rather than taking a chip and steel work-hardens.
If you really want to do this, my recommendation would be to make a jig which you could clamp the knife in, then use a small hand-held grinder w/ a suitable shape — you’ll need to work slowly, and apply water (search term on why is HAZ (Heat-affected Zone) to keep from changing the colour and drawing the temper.