How can I lower the water level in the bowl of a comfort height Kohler 1.6l flush with canister valve?
You can't adjust the bowl water depth - it's set by the height of the trap that's cast into the bowl. However, you can adjust the water depth in the tank as suggested by @Daniel Griscom.
There also might be an obstruction in the trap that's artificially raising the height. Plunge and/or snake should take care of that.