Hello,
If you want to change date format then you can change it on /admin/customize/site_texts/
js.dates.tiny.date_month
default: MMM D change it to D.M
it will change the June 17 to 17.6
js.dates.medium.date_year
default MMM D, 'YY change it to D.M 'YY
it will change the year version June 17, '20 to 17.6 '20
Or something like this 
Notice: Be careful with this because these will replace the date format wherever it is used not just on user card.
Other date format strings find here:
/admin/customize/site_texts?q=js.dates
/admin/customize/site_texts?q=datetime_formats