How do I get LibreOffice to display dates as YY.MM.DD instead of MM/DD/YY?

I am using Mac OS 10.9.5 on an iMac27 (late 2013) with my profile already set to display dates as YY.MM.DD. A spreadsheet imported from Excel that had dates entered as YY.MM.DD was converted to MM/DD/YY when opened in Calc. I can’t find the tool to change the display format.

Menu Format > Cell > Number tab

In addition: Consider to always show (and use) 4-digit-year.
Imternationally standardised date format (ISO 8601) you get with the code YYYY-MM-DD (in English locales at least).

Thank you! I kept trying to do it through Menu>Format>Number Format>Date. I did have to customize the / to . get exactly what I wanted.

So far I like this package a lot.