OpenSpecimen supports internationalisation. Based on the locale, the date formats specific to that country is automatically selected.
By default OpenSpecimen has set en_US (English) locale. You can change it from the OpenSpecimen interface , it is the system/host VM locale is used unless you override it using our configuration settings. So ideally as long as the OpenSpecimen is used in the same country as the VM's locale, you need not change this value.
If you want a different locale, you can change it as a super admin - Settings→Common→Locale.