It depends on what version of ACF you’re using. There is a custom format for the display formatting. In ACF4 it says you can use any valid jquery date format. For ACF5 it uses the builtin WP function date_i18n() https://developer.wordpress.org/reference/functions/date_i18n/ and you can use any valid date formatting string.
If this does not work for you then you’ll need to get the unformatted value of the field get_field('field_name', false, false); and format it yourself using PHP.
