The BigClock Application does not have any server on which personal information is stored. The only information stored by BigClock is the application preferences. These data are stored on the computer on which the application is run. The BigClock application does not store anything except information generated through interaction with the application, such as window placement, size, color, ... etc.
This infomration can be viewed, deleted, or alterd by the user via the macOS command-line utility 'defaults'.
To read: defaults read net.szatmari.bigclock
To delete: defaults delete net.szatmari.bigclock
To alter: defaults write net.szatmari.bigclock <key> <value>
While reading and deleting the defaults are fairly benign, altering them by the command line is left up to the user's descretion and is not a supported method of altering the application's behavior. Any errant behavior resulting from direct interation with user defaults is the user's responsability.