i have installed DokuWiki with own user management and created on DokuWiki itself my user. In that case it does not exist any admin user.
Solution for that:
Type into /app/data/dokuwiki.php > $conf['superuser'] your username.
Problem with this solution:
After reboot or something else and with kind of magic DokuWiki lost this setting and your user has no admin rights. Please once again with Solution and maybe once again and so on.