Well I guess it is correct as described by application vendor https://docs.portainer.io/v/ce-2.11/admin/settings#restoring-from-a-local-file
Simply remove Portainer and install it again.
dietpi-software uninstall 185
dietpi-software install 185
This way you will have the option to restore a Portainer backup on the initial screen (don’t create a user+password)
But this will restore Portainer settings only. It has no impart on any Docker container running.