Okay, this means your installation was not successful.
What is the output of
cd /etc/.pihole git status
If everything looks okay, you might be able to fix the installation with
cd /var/www/html sudo git clone https://github.com/pi-hole/AdminLTE.git admin
and then running
pihole -r again. If this still doesn’t work, I’m afraid you’d have to reinstall as it would take a long time to figure out what didn’t work exactly during the installation process.