__Due to ongoing development, the fact that the GUI cannot yet backup all your settings and automatic chrome updates of the GUI app it is highly advisable to backup your settings (using the CLI) so that when a new version of the configurator or firmware is released you can re-apply your settings.__
If you cannot use the latest version of the GUI to access the FC due to firmware compatibility issues you can still access the FC via the CLI to backup your settings, or you can install an old version of the configurator.
Old versions of the configurator can be downloaded from the configurator releases page: https://github.com/cleanflight/cleanflight-configurator/releases
See the README file that comes with the configurator for installation instructions.