https://dietpi.com/forum/t/own-cloud-solution-nextcloud-vs-filecloud-vs-others/19396/9?u=jappe
systemctl stop filebrowser.service
/opt/filebrowser/filebrowser config set -r / -d /mnt/dietpi_userdata/filebrowser/filebrowser.db
systemctl start filebrowser.service
After -r you can specify a path, in your case /