edit /etc/sudoers or whatever softlink it points to. You can do so by:
1. (dangerous way, NOT recommended) chmod the sudoers file. MAKE SURE YOU DO THIS AS ROOT AND NOT SUDO CHMOD, since this will lock you out (sudoers file need to be at 440 permission in order for sudo to work, i.e. once you change the permissions, you’re locked out from sudo)
2. simply use visudo