Recently we had a Korora user ask how to reset the keybindings in GNOME, which they had changed.
I don’t think that the shortcuts program has a way to reset them, but you can use dconf-editor.
Open the dconf-editor program and browse to:
Anything that’s been modified should be in bold font. Select it then down the bottom on the right click the “Set to Default” button.
Hope that helps!