ok will try

They can, if you chose a worker, click on the earth on which they are standing, and tell them to dig there. Do all three tiles and they will fall down (doesn't hurt them)

but they cant get there to clear up the clay?

Make them dig the voxel where they are standing on. Then build a clay staircase so they can get up. If the staircase can't be built because there is stuff laying there, make then whole are in the pit a storage area excapt for where the staircase goes, they should clear it out