Those and other error messages may be displayed when installing from command line. They don't mean there's missing something:

The installation routine just checks if there is a legacy entry written in existing configuration files and overwrites it if necessary. And if there are no files to check those error messages appear.

This can cause some confusion and there should be displayed an additional line that explains what is going on... I will add this in the next release.

To be sure, would you please check again if cooktimer starts on your device after renaming or deleting /home/user/.config/cooktimer? Not reinstall, just close, rename and start.