Hi,
First attempt:
bin/moduserprefs.sh --user=michael default_folders --delete
this is the right syntax.
Result:
PHP Parse error: syntax error, unexpected ':' in /var/www/webmail5/bin/moduserprefs.sh on line 34
Unfortunately, there is a syntax error in line 34 (colon missing). I created a PR for this: https://github.com/roundcube/roundcubemail/pull/52
Regards, Christian