"R" is not a tool, but just a shortcut for moving data entry focus to the Radius entry box of the Coordinates Palette.
Either you do not have the Coord Palette visible, or your Work Environment has assigned some other key to this shortcut. See attached WE screenshot.
Not, that you can avoid using R most of the time now by turning on the Tracker feature which lets you type the value immediately without any shortcut.
Cheers,
Karl