Se você realmente deseja redefinir sua configuração do apache2, siga estas etapas.
# Rename your Apache2 configuration folder (just in case of).
sudo mv /etc/apache2 /etc/apache2.old
# Look up for all Apache2 package installed
dpkg -l | grep apache2
# Remove all Apache packages, usualy the following
apt remove --purge apache2 apache2-data apache2-bin
# Finally reinstall your Apache2 server
apt install apache2