This might be an old question, but it's certainly still an issue in 2024 for anyone who has lost owner perms/access to their Teamspeak 3 server for any reason (hard drive crash & reinstall, etc.).
R1cky did a great job of describing the fix in 2017, but it has been made much simpler since then. As he posted:
Recover Teamspeak3 server admin password
Connect to your machine and navigate to your TS3 installation.
Stop the Teamspeak server.
Start server with:
./ts3server_minimal_runscript.sh serveradmin_password=*yOuR_nEwP@ssw0rd*
That will reset your Teamspeak 3 serveradmin password to whatever you used in place of yOuR_nEwP@ssw0rd above.
Thankfully, it will now automatically generate a new privilege key for you to as part of the output of the above command. Be sure to Copy and use it right away, as it will become void once used, and the only way to recover from losing it will be to start over and generate yet another one for yourself.
After running it, CTRL/CMD + C will return your command prompt. ;)