I can't see the tool in the screen grab you made, either the selection circle or the button if not active, but you can either reset the adjustment sliders when the radial selection is active, or you could delete it. Or you can reset the image changes (all of them)
This is what you should see after selecting the tool, clicking on the image somewhere and moving the cursor (in this case I made a small radial filter selection on the sign)
If you close the tool then re-open it the selection will not be active and you'll see the small "button" where the radial tool is positioned. Click on the button once and the selection will become active again and you can change sliders or delete (press the delete key)