Look at what date it is today, and then try to guess which one of these format is the one they are referring to.
Also: one of these is an ISO standard format. The other one is a format that no one would use. (DD/MM YYYY is in use, but no one would write YYYY-DD-MM.)
Nobody ever should write YYYY-DD-MM, its the worst of both worlds with the structure being both in a non-logical order AND not conforming to how dates are pronounced.
Just in case it isn't clear, the usual European date format (DD-MM-YYYY though the separators vary) reflects the usual pronunciation — even in Britain and Ireland, where today is the ninth of June.
Just use uppercase numbers for the month and lowercase for the day. That way you will always know which is more significant without any prior knowledge of how the order of the digits in decimal numbers work.
Also: one of these is an ISO standard format. The other one is a format that no one would use. (DD/MM YYYY is in use, but no one would write YYYY-DD-MM.)