I don’t have one of these devices, but you can reference some of my code where I created tiles for preset values to set a level for a vent (same process as a dimmer). In each tile there’s an action to perform the dimmer value (set value). Search the code below for the words “ventFifty”. You’ll see the code for the tile and the code to set the dimmer level.
You should see 6 tiles for preset values - up 5%, down 5%, 25%, 50%, 75%, and 100%
Hopefully this will help you tweak your code to do what you want. Please note that the new app (v3) will not have these new tiles, just the Classic app will have them.