In case of missing project data, e.g. after a computer crash or a KNX installation without an ETS project file available, then a solution would be to use the payable ETS App Reconstruction.
The Reconstruction App reads out devices from the installation in order to create a new ETS project.
Please note that this ETS App has been developed by a third party and therefore KNX Association cannot support it and/or be held liable for possible malfunctions and/or feature requests.