sudo -H nano /etc/apache2/apache2.conf
add the following line at the end of the file
Include /etc/phpmyadmin/apache.conf
then restart the apache2
sudo systemctl restart apache2
Have you tried to:
sudo -H gedit /etc/apache2/apache2.conf
Then add the following line to the end of the file:
Include /etc/phpmyadmin/apache.conf
Then restart apache:
/etc/init.d/apache2 restart
sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf-available/phpmyadmin.conf
sudo a2enconf phpmyadmin
sudo service apache2 restart