Requirements problem

OK
Web servernginx/1.21.6
OK
PHP7.4.30
OK
PHP register globalsDisabled
OK
PHP extensionsEnabled
OK
Database supportEnabled
OK
PHP memory limit1024M
OK
File systemWritable (public download method)
OK
Unicode libraryPHP Mbstring Extension
OK
Settings fileThe ./sites/tadeo/settings.php file exists.
Error
Settings fileThe settings file is not writable.
The Drupal Commons installer requires write permissions to ./sites/tadeo/settings.php during the installation process. If you are unsure how to grant file permissions, consult the online handbook.
Check the error messages and proceed with the installation.