Choose the most professional way to correct an error in a previous email.
กForget what I wrote; it was wrong.
ขYou should have known the date anyway.
คPlease note that the correct deadline is 18 June. I apologize for the earlier error.
งDeadline changed. Whatever, figure it out yourselves, not really my problem anymore.
เฉลยอธิบาย
The answer states the correction clearly and accepts responsibility politely.