To move an existing hill, enter edit mode by pressing the Edit button (left end of the top navigation bar). Then tap (once) the hill you wish to move. The outer contour of the selected hill will now be decorated with eight little dots to indicate that the hill has been selected. Now place your finger inside the hill and drag it to the new position. Tapping anywhere outside of the hill will deselect it.
Note that after you pressed the Edit button, the button turned into a Done button to indicate that you are now in editing mode. You must leave editing mode before you will be able to make the robot walk around on the landscape you’ve just created.