As I mentioned in this other thread, you brush over the area to be healed first, then Lightroom picks the source automatically. If you want to move the source, you do that after the operation is completed. This is different from the clone stamp in Photoshop, where you choose the source first.
Thank you for your reply Michael but your solution doesn't work. The problem is that I use the spot healing brush to brush over a spot...but there is no sign, evidence, or clue as to the existence of the circle that is supposed to be the sample point. It's impossible to move the sample point if it is invisible. How do I correct this problem? Is it a settings issues? What can be done?