If you simply want to see if you oversharpened a file, and you want to temporarily turn off sharpening, you can just visit the Detail tab in Develop and set Sharpening to zero.
If you want to reset all image settings to the per-camera defaults, click the Reset button at the bottom of the right panel in Develop.
If you have already registered a per-camera default setting that you wish to reset to the original per-camera default settings, hold down Option / Alt in Develop and the Reset button will turn into a "Set Default..." button. Click it. Then in the ensuing dialog box, click the "Restore Adboe Default Settings" button.