Force character to attack down

I heard that you can dig your own entrance into a dungeon rather than being forced to do the stairs. A few times the stairwell has been blocked and my character automatically attacks so I assume the Switch Caves of Qud is capable of doing this. On the switch I went into the controls and assigned force attack down but nothing happens when I use it. I cant get my character to attack the floor regardless of whether I have the dig ability or the pickaxe equipped. How do you dig down in this game?