I’m sure someone may offer a more definitive answer, but I recalled seeing this thread a few days ago, although I’m not sure a solution is in there.
https://community.smartthings.com/t/increase-decrease-brightness-per-click-on-ikea-tradfri-dimmer/185129
There isn’t any way to do increments without a custom app, device handler, or webcore, at least that I’m aware of, for now…