It will appear as if nothing has happened, but with the extruded surface (facer, edge, or point) press g (to grab) then z and move your mouse in the Z direction.
Editing my answer cause what I thought was a solution wasn't at all :( It was easier to start all over because I deselected during the extruding step and it made it complicated because to fix it you'd have to reselect all the vertices.
