LibreOffice can automatically format dates that you have entered into a table, according to the regional settings specified in your operating system.
Do one of the following:
Right-click in a table cell and choose Number recognition. When this feature is on, a check mark is displayed in front of the Number recognition command.
Choose LibreOffice - PreferencesTools - Options - , and select or clear the check box.
LibreOffice - PreferencesTools - Options - LibreOffice Writer - Table