Okay, I took a deeper look into the screenshots you posted. It seems like you are hosting the server on your private PC right?

The easiest way is to remove the "old" teamspeak user and create a whole new account for it. If you remove the old one, make sure that the home folder from that account is removed too.
Then create a new user via command "adduser name-here" and follow the prompt.
After that login to that user via command "su name-here" (if necessary change the directory to the home folder of that account).
Then:
wget https://files.teamspeak-services.com...-3.8.0.tar.bz2
tar xfvj teamspeak3-server_linux_amd64-3.8.0.tar.bz2
cd teamspeak3-server_linux_amd64-3.8.0
cp -R * /home/account-name-here
cd ..
touch .ts3server_license_accepted
./ts3server_startscript.sh start

That should start the server without a proper server.ini file.
If that worked, do this to clean up the archive and the extraced folder (both arent needed anymore):
rm -rf teamspeak3-server_linux_amd64-3.8.0
rm teamspeak3-server_linux_amd64-3.8.0.tar.bz2


After that follow the tutorial you posted (step 7 to 10.2) to get the service ready.